Mirror device comprising drive electrode equipped with stopper function

ABSTRACT

The present invention provides a mirror device, comprising: a plurality of deflectable mirrors; an elastic member for deflectably supporting the mirror; a drive electrode for driving the mirror; a control circuit for giving electric charge to the drive electrode and controlling the deflecting direction of the mirror; and a substrate on which the drive electrode and the elastic member, wherein the drive electrode is placed within an area on the substrate the mirror is projected on, has an outer form constituted by sides approximately in parallel to the outer peripheral lines of the present mirror and by sides approximately parallel to the deflection axis of the present mirror, or a form obtained by dividing the aforementioned outer form into a plurality thereof, and also fills the role of a stopper for regulating the deflection angle of the mirror.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a mirror device (also called “digitalmicromirror device” or “micromirror device”) comprised in a projectionapparatus, et cetera.

2. Description of the Related Art

Even though there are significant advances made in recent years on thetechnologies of implementing electromechanical micromirror devices asspatial light modulators, there are still limitations and difficultieswhen they are employed to provide high quality image displays.Specifically, when the display images are digitally controlled, theimage qualities are adversely affected due to the fact that the image isnot displayed with a sufficient number of gray scales.

Electromechanical micromirror devices have drawn considerable interestbecause of their application as spatial light modulators (SLMs). Aspatial light modulator requires an array of a relatively large numberof micromirror devices. In general, the number of devices requiredranges from 60,000 to several million for each SLM. Referring to FIG. 1Afor a digital video system 1 disclosed in a relevant U.S. Pat. No.5,214,420 that includes a display screen 2. A light source 10 is used togenerate light energy for ultimate illumination of display screen 2.Light 9 generated is further concentrated and directed toward lens 12 bymirror 11. Lens 12, 13 and 14 form a beam columnator to operative tocolumnate light 9 into a column of light 8. A spatial light modulator 15is controlled by a computer 19 through data transmitted over data cable18 to selectively redirect a portion of the light from path 7 towardlens 5 to display on screen 2. The SLM 15 has a surface 16 that includesan array of switchable reflective elements, e.g., micromirror devices32, such as elements 17, 27, 37, and 47 as reflective elements attachedto a hinge 30 that shown in FIG. 1B. When element 17 is in one position,a portion of the light from path 7 is redirected along path 6 to lens 5where it is enlarged or spread along path 4 to impinge the displayscreen 2 so as to form an illuminated pixel 3. When element 17 is inanother position, light is not redirected toward display screen 2 andhence pixel 3 would be dark.

The on-and-off states of micromirror control scheme as that implementedin the U.S. Pat. No. 5,214,420 and by most of the conventional displaysystem imposes a limitation on the quality of the display. Specifically,when applying conventional configuration of control circuit has alimitation that the gray scale of conventional system (PWM between ONand OFF states) is limited by the LSB (least significant bit, or theleast pulse width). Due to the On-Off states implemented in theconventional systems, there is no way to provide shorter pulse widththan LSB. The least brightness, which determines gray scale, is thelight reflected during the least pulse width. The limited gray scaleslead to degradations of image display.

Specifically, in FIG. 1C an exemplary circuit diagram of a prior artcontrol circuit for a micromirror according to the U.S. Pat. No.5,285,407. The control circuit includes memory cell 32. Varioustransistors are referred to as “M*” where “*” designates a transistornumber and each transistor is an insulated gate field effect transistor.Transistors M5, and M7 are p-channel transistors; transistors, M6, M8,and M9 are n-channel transistors. The capacitances, C1 and C2, representthe capacitive loads presented to memory cell 32. Memory cell 32includes an access switch transistor M9 and a latch 32 a, which is thebasis of the static random access switch memory (SRAM) design. Allaccess transistors M9 in a row receive a DATA signal from a differentbit-line 31 a. The particular memory cell 32 to be written is accessedby turning on the appropriate row select transistor M9, using the ROWsignal functioning as a wordline. Latch 32 a is formed from twocross-coupled inverters, M5/M6 and M7/M8, which permit two stablestates. The state 1 is Node A high and Node B low and state 2 is Node Alow and Node B high.

The dual-state switching as illustrated by the control circuit controlsthe micromirrors to position either at an ON of an OFF angularorientation as that shown in FIG. 1A. The brightness, i.e., the grayscales of display for a digitally control image system is determined bythe length of time the micromirror stays at an ON position. The lengthof time a micromirror is controlled at an ON position is in turnedcontrolled by a multiple bit word. For simplicity of illustration, FIG.1D shows the “binary time intervals” when control by a four-bit word. Asthat shown in FIG. 1D, the time durations have relative values of 1, 2,4, 8 that in turn define the relative brightness for each of the fourbits where “1” is for the least significant bit and 8 is for the mostsignificant bit. According to the control mechanism as shown, theminimum controllable differences between gray scales for showingdifferent brightness is a brightness represented by a “least significantbit” that maintaining the micromirror at an ON position.

When adjacent image pixels are shown with great degree of different grayscales due to a very coarse scale of controllable gray scale, artifactsare shown between these adjacent image pixels. That leads to imagedegradations. The image degradations are specially pronounced in brightareas of display when there are “bigger gaps” of gray scales betweenadjacent image pixels. It was observed in an image of a female modelthat there were artifacts shown on the forehead, the sides of the noseand the upper arm. The artifacts are generated due to a technicallimitation that the digital controlled display does not providesufficient gray scales. At the bright spots of display, e.g., theforehead, the sides of the nose and the upper arm, the adjacent pixelsare displayed with visible gaps of light intensities.

As the micromirrors are controlled to have a fully on and fully offposition, the light intensity is determined by the length of time themicromirror is at the fully on position. In order to increase the numberof gray scales of display, the speed of the micromirror must beincreased such that the digital control signals can be increased to ahigher number of bits. However, when the speed of the micromirrors isincreased, a strong hinge is necessary for the micromirror to sustain arequired number of operational cycles for a designated lifetime ofoperation, In order to drive the micromirrors supported on a furtherstrengthened hinge, a higher voltage is required. The higher voltage mayexceed twenty volts and may even be as high as thirty volts. Themicromirrors manufacture by applying the CMOS technologies probablywould not be suitable for operation at such higher range of voltages andtherefore the DMOS micromirror devices may be required. In order toachieve higher degree of gray scale control, a more complicatemanufacturing process and larger device areas are necessary when DMOSmicromirror is implemented. Conventional modes of micromirror controlare therefore facing a technical challenge that the gray scale accuracyhas to be sacrificed for the benefits of smaller and more cost effectivemicromirror display due to the operational voltage limitations.

There are many patents related to light intensity control. These patentsinclude U.S. Pat. Nos. 5,589,852, 6,232,963, 6,592,227, 6,648,476, and6,819,064. There are further patents and patent applications related todifferent shapes of light sources. These patents includes U.S. Pat. Nos.5,442,414 and 6,036,318 and Application 20030147052. The U.S. Pat. No.6,746,123 discloses special polarized light sources for preventing lightloss. However, these patents and patent application do not provide aneffective solution to overcome the limitations caused by insufficientgray scales in the digitally controlled image display systems.

Furthermore, there are many patents related to spatial light modulationthat includes U.S. Pat. Nos. 2,025,143, 2,682,010, 2,681,423, 4,087,810,4,292,732, 4,405,209, 4,454,541, 4,592,628, 4,767,192, 4,842,396,4,907,862, 5,214,420, 5,287,096, 5,506,597, and 5,489,952. However,these inventions have not addressed or provided direct resolutions for aperson of ordinary skill in the art to overcome the above-discussedlimitations and difficulties.

Therefore, a need still exists in the art of image display systemsapplying digital control of a micromirror array as a spatial lightmodulator to provide new and improved systems such that theabove-discussed difficulties can be resolved.

Incidentally, an address electrode for driving a mirror is placed underthe mirror. The reason is that the mirror and address electrode need tobe placed as closely to each other as possible in order to effectivelygenerate a sufficient magnitude of a coulomb force for driving themirror because the coulomb force for driving it is inverselyproportional to the second power of the distance between the electrodeand mirror. Further, the coulomb force is also dependent on the areasize of the address electrode, that is, the coulomb force increases withthe area size of the address electrode. That is, the address electrodewith a sufficient area size needs to be placed under the mirror.

A miniaturization of a mirror device is naturally accompanied by areduction in the space for placing an address electrode. In addition, astopper member is placed under the mirror separately from the addresselectrode for regulating the deflection angle of a mirror by letting itabut the stopper member. In a situation in which the mirror device isminiaturized, causing the space used for placing the address electrodeto become tight, the configuring of the address electrode and a stopperfor determining the deflection angle of the mirror as practiced in theconventional technique will be faced with a technical problem that aspace for placing the address electrode is further reduced, making itvery difficult to obtain a sufficient magnitude of the coulomb force.

FIG. 2 shows the structure for regulating a mirror deflection angle inthe conventional mirror device disclosed in U.S. Pat. No. 5,583,688.This structure comprises a landing yoke 310 which is connected to amirror 300 and which deflects similarly to the mirror 300, with a tip312 formed in a part of the landing yoke 310. The tip 312 contacts witha metallic layer that is different from the address electrode 314 beforethe mirror 300 abuts on the address electrode 314, thereby regulatingthe deflection angle of the mirror 300. In such a configuration, thelanding yoke and tip exist in the space for placing an electrode, makingit difficult to increase the size of the address electrode.

FIG. 3 shows the structure for regulating a mirror deflection angle inthe conventional mirror device disclosed in US Patent Application20060152690. Although this discloses a structure that has eliminated thelanding yoke, a tip determining the deflection angle of a mirror stillexists, as a separate member, in the space for placing an addresselectrode, also making it difficult to increase the size of the addresselectrode.

FIG. 4 shows the structure for regulating a mirror deflection angle inthe conventional mirror device disclosed in U.S. Pat. No. 6,198,180.Also in the mirror device disclosed by the patent, the configurationincludes a stop post which is separate from a capacitor panel and whichregulates the deflection angle of the mirror, and therefore amaximization of the electrode size cannot be carried out.

FIG. 5 shows the structure for regulating a mirror deflection angle inthe conventional mirror device disclosed in U.S. Pat. No. 6,992,810.This configuration comprises a mechanical stop element, which regulatesthe deflection angle of a mirror, directly under the mirror, so that themechanical stop element abuts on a landing electrode that is maintainedat the same potential as the mirror. This disclosure also makes itdifficult to maximize the electrode size. Further, in order to make themirror device using the above described PWM control capable of producinghigher grade of gradations, a drive voltage needs to be higher inkeeping with an increase in the spring constant of the hinge member forimproving the follow-up performance of the mirror, and therefore thedifficulty in attaining higher grade of gradations increases withminiaturization of the mirror device.

SUMMARY OF THE INVENTION

In consideration of the above described problem, the purpose of thepresent invention is to miniaturize a mirror device and provide aprojection apparatus comprising such a mirror device.

A first aspect of the present invention is a mirror device, comprising:a plurality of deflectable mirrors; an elastic member for deflectablysupporting the mirror; a drive electrode for driving the mirror; acontrol circuit for giving electric charge to the drive electrode andcontrolling the deflecting direction of the mirror; and a substrate onwhich the drive electrode and the elastic member are formed, wherein thedrive electrode is placed within an area on the substrate the mirror isprojected on, has an outer form constituted by sides approximately inparallel to the outer peripheral lines of the present mirror and bysides approximately parallel to the deflection axis of the presentmirror, or a form obtained by dividing the aforementioned outer forminto a plurality thereof, and also fills the role of a stopper forregulating the deflection angle of the mirror.

A second aspect of the present invention is the mirror device accordingto the first aspect, wherein the drive electrode is equipped withopposite surfaces which are opposite to the mirror and of which thedistances from the present mirror are different.

A third aspect of the present invention is the mirror device accordingto the first aspect, wherein the drive electrode has a plurality ofsurfaces in parallel to the bottom surface of the mirror.

A fourth aspect of the present invention is the mirror device accordingto the third aspect, wherein the contact part of the drive electrodecontacting with the mirror or a deflection member that deflects with themirror is any of the border parts of the plurality of surfaces of thedrive electrode.

A fifth aspect of the present invention is the mirror device accordingto the first aspect, satisfying the relationship of

d1≧(L1*d2)/L2,

where “L1” is the distance between the edge of the drive electrode on aside close to the deflection axis of the mirror and the presentdeflection axis, “L2” is the distance between the edge of the driveelectrode on a side far from the deflection axis of the mirror and thepresent deflection axis, “d1” is the distance between the bottom surfaceof the mirror on the edge of the drive electrode on a side close to thedeflection axis of the mirror and the drive electrode, and “d2” is thedistance between the bottom surface of the mirror on the edge of thedrive electrode on a side far from the deflection axis of the mirror andthe drive electrode.

A sixth aspect of the present invention is the mirror device accordingto the first aspect, wherein the contact part of the drive electrodecontacting with the mirror or a deflection member that deflects with themirror is anywhere other than the edge of the drive electrode on a sidefar from the deflection axis of the present mirror.

A seventh aspect of the present invention is the mirror device accordingto the first aspect, wherein the drive electrode has a form so that acontact with the mirror or a deflection member that deflects with themirror is a point contact.

An eighth aspect of the present invention is the mirror device accordingto the first aspect, wherein the drive electrode has a form so that acontact with the mirror or a deflection member that deflects with themirror is a line contact.

A ninth aspect of the present invention is the mirror device accordingto the first aspect, wherein the drive electrode has a form so that acontact with the mirror or a deflection member that deflects with themirror is an area contact.

A tenth aspect of the present invention is the mirror device accordingto the ninth aspect, wherein the contact part of the drive electrodecontacting with the mirror or a deflection member that deflects with themirror is a slope surface having the same slope angle as the deflectionangle of the mirror.

An eleventh aspect of the present invention is the mirror deviceaccording to the first aspect, wherein there is a plurality of contactparts of the drive electrode contacting with the mirror or a deflectionmember that deflects with the mirror.

A twelfth aspect of the present invention is the mirror device accordingto the eleventh aspect, wherein a plurality of the contact parts areindividually placed apart from each other by no less than 30% of thedeflection axis length of the mirror.

A thirteenth aspect of the present invention is the mirror deviceaccording to the first aspect, wherein at least a part of the driveelectrode including the contact part contacting with the mirror or adeflection member that deflects with the mirror is covered with aninsulation member, and the dielectric strength voltage of the insulationmember is no less than 2 times the drive voltage of the mirror.

A fourteenth aspect of the present invention is the mirror deviceaccording to the thirteenth aspect, wherein the dielectric strengthvoltage of the insulation member is no less than 3 volts.

A fifteenth aspect of the present invention is the mirror deviceaccording to the first aspect, wherein the mirror has an approximatesquare form, and the deflection axis of the mirror is on the diagonalline thereof.

A sixteenth aspect of the present invention is the mirror deviceaccording to the first aspect, wherein the pitch between the adjacentmirrors is between 4 μm and 10 μm.

A seventeenth aspect of the present invention is the mirror deviceaccording to the first aspect, wherein the deflection angle of themirror is equal to an angle α which is determined by an aperture ratioof a projection optical system satisfying a theoretical resolutiondetermined by the pitch of the adjacent mirrors in a directionprojecting a modulated light to a projection light path, while thedeflection angle is no less than the angle α in a direction other thanthe direction projecting the modulated light to the projection lightpath.

An eighteenth aspect of the present invention is the mirror deviceaccording to the first aspect, wherein at least a part of the driveelectrode including the contact part contacting with the mirror or adeflection member that deflects with the mirror is covered with apassivation material.

A nineteenth aspect of the present invention is the mirror deviceaccording to the eighteenth aspect, wherein the passivation material isa halide.

A twentieth aspect of the present invention is the mirror deviceaccording to the first aspect, wherein at least a part of the driveelectrode is covered with a low reflection material.

A twenty-first aspect of the present invention is the mirror deviceaccording to the first aspect, wherein at least a part of the driveelectrode is covered with a film having a film thickness of ¼ of thewavelength of the visible light.

A twenty-second aspect of the present invention is a projectionapparatus, comprising: a light source; an illumination optical systemfor condensing the illumination light emitted from the light source anddirecting the light; a mirror device array, comprising a plurality ofdeflectable mirror elements, for modulating the illumination lightemitted from the light source; and a projection optical system forprojecting the light modulated by the mirror device array, wherein themirror element includes a mirror and a drive electrode for driving themirror, the deflection angle of the mirror is determined by the apertureratio of the projection optical system satisfying a theoreticalresolution that is determined on the basis of the pitch of the adjacentmirrors, and the drive electrode also fills the function of a stopperfor regulating the deflection angle.

A twenty-third aspect of the present invention is the projectionapparatus according to the twenty-second aspect, wherein the deflectionangle of the mirror is between 2 degrees and 14 degrees relative to thehorizontal state of the present mirror.

A twenty-fourth aspect of the present invention is a projectionapparatus, comprising: a light source; an illumination optical systemfor condensing the illumination light emitted from the light source anddirecting the light; a mirror device array, comprising a plurality ofdeflectable mirror elements, for modulating the illumination lightemitted from the light source; and a projection optical system forprojecting the light modulated by the mirror device array, wherein

the mirror element includes a mirror and a drive electrode for drivingthe mirror, the deflection angle of the mirror is larger than an anglethat is determined by the aperture ratio of the projection opticalsystem satisfying a theoretical resolution that is determined on thebasis of the pitch of the adjacent mirrors, and the drive electrode alsofills the role of a stopper for regulating the deflection angle.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described in detail below with reference to thefollowing Figures.

FIG. 1A is a conceptual diagram showing the configuration of aprojection apparatus according to a conventional technique;

FIG. 1B is a conceptual diagram showing the configuration of a mirrorelement of the projection apparatus according to a conventionaltechnique;

FIG. 1C is a conceptual diagram showing the configuration of the drivecircuit of a mirror element of the projection apparatus according to aconventional technique;

FIG. 1D is a conceptual diagram showing the format of image data used inthe projection apparatus according to a conventional technique;

FIG. 2 is a diagram exemplifying the configuration for regulating amirror deflection angle in a conventional mirror device;

FIG. 3 is a diagram exemplifying the configuration for regulating amirror deflection angle in a conventional mirror device;

FIG. 4 is a diagram exemplifying the configuration for regulating amirror deflection angle in a conventional mirror device;

FIG. 5 is a diagram exemplifying the configuration for regulating amirror deflection angle in a conventional mirror device;

FIG. 6 is a diagonal view diagram showing a mirror device arraying, intwo dimensions on a device substrate, a plurality of mirror elementseach for controlling the reflecting direction of an incident light bydeflecting a mirror;

FIG. 7 is a diagram showing the relationship among the numericalaperture NA1 of an illumination light path, the numerical aperture NA2of a projection light path and the deflection angle of a mirror;

FIG. 8A is an illustration for describing etendue by exemplifying theprojection of an image, by way of an optical device, using a dischargelamp light source;

FIG. 8B is an illustration of projecting an image, by way of an opticaldevice, using a laser light source in the embodiment of the presentinvention;

FIG. 8C is an illustration of projecting an image, by way of an opticaldevice, using a discharge lamp;

FIG. 9A is an upper plain view diagram of a mirror element of a mirrordevice according to the embodiment of the present invention;

FIG. 9B is an outline diagram showing a cross-sectional configuration ofa mirror element of a mirror device according to the embodiment of thepresent invention;

FIG. 9C is an outline diagram showing a cross-sectional configuration ofa mirror element of a mirror device according to the embodiment of thepresent invention;

FIG. 10A is a diagram illustrating diffraction light generating when amirror reflects light;

FIG. 10B is a diagram illustrating diffraction light generating when amirror reflects light;

FIG. 11A is an upper plain view diagram of an exemplary modification ofa mirror element of a mirror device according to the embodiment of thepresent invention;

FIG. 11B is an outline diagram showing a cross-sectional configurationof an exemplary modification of a mirror element of a mirror deviceaccording to the embodiment of the present invention;

FIG. 12 is an outline diagram of a cross-section of a mirror element ofa mirror device according to the embodiment of the present invention;

FIG. 13A is an upper plain view diagram showing another form of anelectrode comprised in a mirror element of a mirror device according tothe embodiment of the present invention;

FIG. 13B is a side view diagram showing another form of an electrodecomprised in a mirror element of a mirror device according to theembodiment of the present invention;

FIG. 14 is a diagram showing another form of an electrode comprised in amirror element of a mirror device according to the embodiment of thepresent invention;

FIG. 15 is a diagram showing another form of an electrode comprised in amirror element of a mirror device according to the embodiment of thepresent invention;

FIG. 16A is an upper plain view diagram showing another form of anelectrode comprised in a mirror element of a mirror device according tothe embodiment of the present invention;

FIG. 16B is a side view diagram showing another form of an electrodecomprised in a mirror element of a mirror device according to theembodiment of the present invention;

FIG. 17 is a diagram showing another form of an electrode comprised in amirror element of a mirror device according to the embodiment of thepresent invention;

FIG. 18A is a diagram showing another form of an electrode comprised ina mirror element of a mirror device according to the embodiment of thepresent invention;

FIG. 18B is a diagram showing another form of an electrode comprised ina mirror element of a mirror device according to the embodiment of thepresent invention;

FIG. 19A is a diagram showing another form of an electrode comprised ina mirror element of a mirror device according to the embodiment of thepresent invention;

FIG. 19B is a diagram showing another form of an electrode comprised ina mirror element of a mirror device according to the embodiment of thepresent invention;

FIG. 20A is a diagram showing another form of an electrode comprised ina mirror element of a mirror device according to the embodiment of thepresent invention;

FIG. 20B is a diagram showing another form of an electrode comprised ina mirror element of a mirror device according to the embodiment of thepresent invention;

FIG. 20C is a diagram showing another form of an electrode comprised ina mirror element of a mirror device according to the embodiment of thepresent invention;

FIG. 21 is a conceptual diagram exemplifying a layout of the internalconfiguration of a mirror device according to the embodiment of thepresent invention;

FIG. 22A is a diagram depicting a state in which an incident light isreflected toward a projection optical system by deflecting the mirror ofa mirror element;

FIG. 22B is a diagram depicting a state in which an incident light isreflected not toward a projection optical system by deflecting themirror of a mirror element;

FIG. 22C is a diagram delineating a state in which reflecting and notreflecting an incident light toward a projection optical system arerepeated by free-oscillating the mirror of a mirror element;

FIG. 23 is a chart showing the transition response between the ON stateand OFF state of a mirror of a mirror device;

FIG. 24A shows a cross-section of a mirror element equipped with onlyone address electrode and drive circuit, respectively, corresponding tothe one mirror element, as another exemplary embodiment of a mirrorelement;

FIG. 24B is an outline diagram of a cross-section of the mirror elementshown in FIG. 24A;

FIG. 25A is the plain view diagram and cross-sectional diagram of amirror element configured so that the area size S1 of the firstelectrode part of one address electrode and the area size S2 of thesecond electrode part thereof is in the relationship of S1>S2, and sothat the connection part between the first and second electrode partsexists in the same layer as they both do;

FIG. 25B is the plain view diagram and cross-sectional diagram of amirror element configured so that the area size S1 of the firstelectrode part of one address electrode and the area size S2 of thesecond electrode part thereof is in the relationship of S1>S2, and sothat the connection part between the first and second electrode partsexists in a layer different from the layer in which they both do;

FIG. 25C is the plain view diagram and cross-sectional diagram of amirror element configured so that the area size S1 of the firstelectrode part of one address electrode and the area size S2 of thesecond electrode part thereof is in the relationship of S1=S2, and sothat the distance G1 between the mirror and the first electrode and thedistance G2 between the mirror and the second electrode is in therelationship of G1<G2;

FIG. 26 is a diagram showing a data input to the mirror element shown inFIG. 25A, application of a voltage to an address electrode and thedeflection angle of the mirror, in a time series;

FIG. 27 is an illustrative cross-sectional diagram depicting a situationof reflecting an f/10 light flux possessing a coherent characteristicfor a mirror device configured such that the deflection angles of themirror in ON light state and OFF light state are designated as ±3degrees, respectively;

FIG. 28A is a front cross-sectional diagram of an assembly body thatpackages two mirror devices using a package substrate;

FIG. 28B is a plain view diagram of the assembly body shown in FIG. 31Awith the cover glass and intermediate member removed;

FIG. 29A is a front view diagram of a two-panel projection apparatuscomprising a plurality of mirror devices packaged in a single package;

FIG. 29B is a rear view diagram of the two-panel projection apparatusshown in FIG. 32A;

FIG. 29C is a side view diagram of the two-panel projection apparatusshown in FIG. 32A;

FIG. 29D is a plain view diagram of the two-panel projection apparatusshown in FIG. 29A;

FIG. 30 is a conceptual diagram showing the configuration of asingle-panel projection apparatus according to the embodiment of thepresent invention;

FIG. 31A is a conceptual diagram showing the configuration of amulti-panel projection apparatus according to the embodiment of thepresent invention;

FIG. 31B is a conceptual diagram showing the configuration of anexemplary modification of a multi-panel projection apparatus accordingto the embodiment of the present invention;

FIG. 31C is a conceptual diagram showing the configuration of anotherexemplary modification of a multi-panel projection apparatus accordingto the embodiment of the present invention;

FIG. 32 is a block diagram showing a control unit for a projectionapparatus according to the embodiment of the present invention;

FIG. 33A is a conceptual diagram showing the data structure of imagedata used in a single-panel projection apparatus according to theembodiment of the present invention;

FIG. 33B is a conceptual diagram showing the data structure of imagedata used in a multi-panel projection apparatus according to theembodiment of the present invention;

FIG. 34A is a chart exemplifying a control signal used in a projectionapparatus according to the embodiment of the present invention;

FIG. 34B is a chart exemplifying another control signal used in aprojection apparatus according to the embodiment of the presentinvention;

FIG. 34C is a chart showing, in enlargement, a part of a control signalused in a projection apparatus according to the embodiment of thepresent invention;

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First is a description of an outline of an example of a mirror deviceaccording to a preferred embodiment of the present invention.

[Outline of the Device]

The first is a description of a mirror device.

Projection apparatuses each generally using a spatial light modulator,such as a transmissive liquid crystal, a reflective liquid crystal, amirror array and the like, are widely known.

A spatial light modulator is formed as a two-dimensional array arrangingfrom tens of thousands to millions of miniature modulation elements,with the individual elements enlarged and displayed, as the individualpixels corresponding to an image to be displayed, onto a screen by wayof a projection lens.

The spatial light modulators generally used for projection apparatusesprimarily include two types, i.e., a liquid crystal device formodulating the polarizing direction of incident light by sealing aliquid crystal between transparent substrates and providing them with apotential, and a mirror device deflecting miniature micro electromechanical systems (MEMS) mirrors with electrostatic force andcontrolling the reflecting direction of illumination light.

One embodiment of the above described mirror device is disclosed in U.S.Pat. No. 4,229,732, in which a drive circuit using MOSFET anddeflectable metallic mirrors are formed on a semiconductor wafersubstrate. The mirror allows to be deformed by electrostatic forcesupplied from the drive circuit and is capable of changing thereflecting direction of the incident light.

Meanwhile, U.S. Pat. No. 4,662,746 has disclosed an embodiment in whichone or two elastic hinges retain a mirror. If the mirror is retained byone elastic hinge, the elastic hinge functions as bending spring. If themirror is retained by two elastic hinges, they function as torsionsprings to incline the mirror and thereby the reflecting direction ofthe incident light is deflected.

Next is an outline description of the configuration of the mirrordevice.

FIG. 6 is a diagonal view diagram of a mirror device arraying, in twodimensions, a plurality of mirror elements that control the reflectingdirection of incident light by deflecting mirrors.

As shown in FIG. 6, the mirror device 4000 is constituted by arraying,crosswise in two dimensions on a device substrate 4004, a plurality ofmirror elements each comprising address electrodes (not shown here),elastic hinge (not shown here), and a mirror 4003 supported by theelastic hinge. In the configuration shown in FIG. 6, plural mirrorelements 4001, each of which comprises a square mirror 4003, are arrayedcrosswise in constant intervals on the device substrate 4004.

The mirror 4003 of one mirror element 4001 is controlled by applying avoltage to the address electrode provided on the device substrate 4004.

The mirror driven by a drive electrode abuts on a landing electrodestructured differently from the drive electrode, and thereby aprescribed tilt angle is maintained. A “landing chip”, which possesses aspring property, is formed on the contact part abutting on the landingelectrode so that an operation of the mirror deflecting to the reversedirection upon changing over the control is assisted. The part formingthe landing chip and the landing electrode are maintained at the samepotential so that the contact will not cause a shorting or the like.

[Outlines of Mirror Size and Resolution]

Next is an outline description of the size of a mirror and theresolution.

The size of a mirror for constituting such a mirror device is between 4μm and 10 μm for each side, and the mirrors are placed on asemiconductor wafer substrate in such a manner as to minimize the gapbetween adjacent mirrors so that useless reflection light from the gapdoes not degrade the contrast of a modulated image.

Further specifically, the ratio (noted as “aperture ratio” hereinafter)of the effective reflection surface to the pixel placement region iscommonly set at as approximately no less than 80%, with the reflectionratio approximately designated at no lower than 80%. The gap betweenadjacent mirrors are preferred to be set as a minimum while avoiding thephysical interference, which is specifically designated as, for example,between 0.15 μm and 0.55 μm. Such a mirror device with the apertureimproved as described above makes it possible to reduce the energyirradiated on the device substrate through the gap between the adjacentmirrors and accordingly alleviate an operational failure, and the like,due to an extraneous heating and a photoelectric effect.

One mirror device is constituted by forming on a substrate anappropriate number of mirror elements, as image display elements,comprising these mirrors. Here, the appropriate number as image displayelements are the numbers, for example, in compliance to the resolutionof a display specified by the Video Electronics Standards Association(VESA) and to the television forecasting standard. Here, in the case ofconfiguring a mirror device comprising the number of mirror elements,which is compliant to the WXGA (with the resolution of 1280×768)specified by the VESA and in which mirrors are arrayed in intervals(noted as “pitch” hereinafter) of 10 μm, a sufficiently miniature mirrordevice is configured, with about 15.49 mm (0.61 inches) of the diagonallength of the display area.

[Outline of the Introduction of Laser Light Source]

Next is an outline description of the introduction of a laser lightsource. In a projection apparatus using the above described mirrordevice as a display device, there is a close relationship among thenumerical aperture (NA) NA1 of an illumination light path, the numericalaperture NA2 of a projection light path and the tilt angle α of amirror. FIG. 7 shows the relationship among them.

Let it be assumed that the tilt angle α of a mirror 4003 as 12 degrees.When a modulated light reflected by the mirror 4003 and incident to thepupil of the projection light path is set at the perpendicular directionof a device substrate 4004, the illumination light is incident from adirection inclined by 2α, that is, 24 degrees, relative to theperpendicular of the device substrate 4004. For the light beam reflectedby the mirror to be most efficiently incident to the pupil of theprojection lens, the numerical aperture of the projection light path isdesirably equal to the numerical aperture of the illumination lightpath. If the numerical aperture of the projection light path is smallerthan that of the illumination light path, the illumination light cannotbe sufficiently imported into the projection light path, while if thenumerical aperture of the projection light path is larger that that ofthe illumination light path, the illumination light can be entirelyimported; the projection lens becomes unnecessarily large, bringingabout inconvenience in terms of configuring the projection apparatus.Further in this event, the light fluxes of the illumination light andprojection light need to be basically placed apart from each otherbecause the optical members of the illumination system and those of theprojection system need to be physically placed respectively.

It is possible to reduce an extraneous space between the light flux ofthe illumination light and that of the projection light by designing alayout so as to cause the aforementioned two light fluxes to be adjacentto each other as exemplified in FIG. 7.

From the above considerations, when a mirror device with the tilt angleof a mirror being 12 degrees is used, the numerical aperture (NA) NA1 ofthe illumination light path and the numerical aperture NA2 of theprojection light path are preferred to be set as follows:

NA1=NA2=sin α=sin 12°

Letting the F number of the illumination light path be Fa and the Fnumber of the projection light path be Fb, then the numerical aperturecan be converted into an F number as follows:

Fa=Fb=1/(2*NA)=1/(2*sin 12°)=2.4

In order to maximize the importation of illumination light emitted froma light source possessing non-directivity in the emission direction oflight, such as a high-pressure mercury lamp and xenon lamp, which aregenerally used for a projection apparatus, there is a requirement formaximizing the importing angle of light on the illumination light pathside. Considering that the numerical aperture of the illumination lightpath is determined by the specification of the tilt angle of a mirror tobe used, it is clear that the tilt angle of the mirror needs to be largefor increasing the numerical aperture of the illumination light path.

The increasing of the tilt angle of the mirror, however, ushers in theproblem of requiring a higher drive voltage for driving the mirror.Should the tilt angle of the mirror be increased, the distance betweenthe mirror and an electrode for driving the mirror needs to be increasedin order to secure a physical space for the mirror to be tilted.

The electrostatic force F generated between the mirror and electrode isgiven by the following expression:

F=(∈*S*V ²)/(2*d2),

where “S” is the area size of the electrode, “V” is a voltage, “d” isthe distance between the electrode and mirror and “∈” is thepermittivity of vacuum.

The expression makes it comprehensible that the drive force is decreasedin proportion to the second power of the distance d between theelectrode and mirror. It is conceivable to increase the drive voltagefor compensating the decrease in the drive force associated with theincrease in the distance; conventionally, however, the drive voltage isabout 5 to 10 volts in the drive circuit by means of a CMOS process usedfor driving a mirror and therefore a relatively special process such asa DMOS process is required if a drive voltage in excess of about 10volts is needed. That is not preferable in view of the purchase of amirror device and the cost reduction.

Further, as for a cost reduction of a mirror device, it is desirable toobtain as many mirror devices as possible from a single semiconductorwafer substrate in view of the improvement of productivity. That is, aminiaturization of the pitch between mirror elements reduces the size ofthe mirror device per se. It is clear that the area size of an electrodeis reduced in association with the miniaturization of the mirror, whichalso leads to less driving power.

Furthermore, in contrast to the requirement for miniaturizing a mirrordevice, there is a problem in which the larger a mirror device, thebrighter is it possible to illuminate as long as a conventional lamp isused because a conventional lamp with a non-directivity in its emissionallows the usage efficiency of light to be substantially reduced. Thisis attributable to a relationship commonly called etendue.

As exemplified in FIG. 8A, when a device 4107 is illuminated from alight source 4150 by way of a light source lens 4106 and a projectionimage 4109 is formed via a projection lens 4108, the followingexpression is applied:

y*u=y′*u′,

where “y” is the size of the light source, “u” is the import angle oflight on the light source side, “y′” is the size of a light source imageand “u′” is the converging angle on the image side.

That is, the smaller the device on which a light source is attempted tobe imaged, the smaller the import angle on the light source sidebecomes. This results in sacrificing the brightness of the projectionimage.

Accordingly, the embodiment of the present invention is configured touse a laser light source 4200 with strong directivity of the emissionlight for the light source as exemplified in FIG. 8B. The use of thelaser light source 4200 makes it possible to obtain a sufficient amountof energy even if the import angle of light on the light source side isdesignated as smaller, as exemplified in FIG. 8B, than in the case of aconventional lamp 4105 without directivity as exemplified in FIG. 8C.This configuration, using the laser light source 4200 as the lightsource likewise the case of the present embodiment, attains a projectionapparatus capable of securing a sufficient level of brightness even whena miniaturized mirror device 4108 is used.

[Outline of Resolution Limit]

Next is an outline description of a resolution limit.

An examination of the limit value of the aperture ratio of a projectionlens used for a projection apparatus, which displays the display surfaceof a mirror device in enlargement, in view of the resolution of an imageto be projected, leads to the following.

Where “Rp” is the pixel pitch of the mirror device, “NA” is the apertureratio of a projection lens, “F” is an F number and “λ” is the wavelengthof light, the limit “Rp” with which any adjacent pixels on theprojection surface are separately observed is given by the followingexpression:

Rp=0.61*λ/NA=1.22*λ*F

When the pitch between mirror elements is shortened by using aminiaturized mirror, the relationship among the aperture ratio NA, whichis theoretically required for resolving individual mirrors, the F numberfor the projection lens and the corresponding deflection angle of themirror is given by the following tables for the wavelength of light atλ=400 nm, the green light (at λ=650 nm) and the red light (at λ=800 nm),respectively.Tables: The NA required for resolving, in the projected image, adjacentmirror elements and the tilt angle of a mirror for separating theillumination light and projection light with the respective NA: at λ=400nm

Mirror Deflection device pixel Aperture F number for angle of mirror:pitch: μm ratio: NA projection lens degrees 4 0.061 8.2 3.49 5 0.04910.2 2.79 6 0.041 12.3 2.33 7 0.035 14.3 2.00 8 0.031 16.4 1.75 9 0.02718.4 1.55 10 0.024 20.5 1.40 11 0.022 22.5 1.27

At λ = 650 nm Mirror Deflection device pixel Aperture F number for angleof mirror: pitch: μm ratio: NA projection lens degrees 4 0.099 5.0 5.675 0.079 6.3 4.54 6 0.066 7.6 3.78 7 0.057 8.8 3.24 8 0.050 10.1 2.84 90.044 11.3 2.52 10 0.040 12.6 2.27 11 0.036 13.9 2.06

At λ = 800 nm Mirror Deflection device pixel Aperture F number for angleof mirror: pitch: μm ratio: NA projection lens degrees 4 0.122 4.1 6.975 0.098 5.1 5.58 6 0.081 6.1 4.65 7 0.070 7.2 3.99 8 0.061 8.2 3.49 90.054 9.2 3.11 10 0.049 10.2 2.79 11 0.044 11.3 2.54

Based on the above tables, it is understood that a sufficient F numberfor a projection lens required for resolving, in the projected image,individual pixels with, for example 10 μm pixel pitch is theoreticallyF=20.5, an extremely small aperture, when the wavelength of illuminationlight is λ=400 nm. A sufficient deflection angle of mirror in this caseis mere 1.4 degrees, indicating that the drive voltage for the mirror isextremely low.

However, the using of an illumination lens matching such a projectionlens and of a conventional lamp with no directivity makes it impossibleto secure a sufficient level of brightness in the image. Accordingly,the use of a laser light source, avoiding the above described problemattributable to the etendue, makes it possible to increase the F numberfor the illumination and projection optical systems to the numberindicated in the table and also reduce the deflection angle of a mirrorelement as a result, thus enabling configuring a compact mirror devicewith a low drive voltage.

Further, the introducing of a laser light source as in the presentembodiment provides the benefit as follows. That is, the lowering of adrive voltage by introducing the laser light source makes it possible tofurther reduce the thickness of the circuit wiring pattern of a controlcircuit provided for controlling a mirror. Here, setting the deflectionangle of the mirror at a minimum for each frequency of light as thetarget of modulation, it is possible to further reduce the powerconsumption. That is, the deflection angle of the mirror can be smallerfor a mirror device for modulating, for example, the blue light than thedeflection angle of a mirror for the mirror device for modulating thered light. This fact means a possibility that, when, for example, singlecolor laser light sources are used for light sources, the respectiveillumination light paths are individually provided and the optimal NAsare set for the respective illumination light paths, and thereby aprojection apparatus can be configured without requiring increases inthe sizes of optical components used in the apparatus.

Further, it is possible to cause the laser light source to perform pulseemission by comprising a circuit that emits the pulse emission of ON andOFF lights alternately for a predetermined period. Controlling the pulseemission of the light source makes it possible to adjust intensity inaccordance with the image signal (that is, in accordance with thebrightness and hue of the entire projection image) and to finely expressthe gradations of the display image. Further, lowering the output of thelaser light makes it possible to make the dynamic range of an imagevariable and darken the entire screen in response to a dark image.

Furthermore, performing a pulse control makes it possible to turn OFF alaser light source as appropriate during a non-image display period orduring a period for changing over the colors of a display image in oneframe. As a result, a temperature rise due to the irradiation withextraneous light onto a mirror device can be alleviated.

Next is a description, in detail, of a first preferred embodiment of thepresent invention with the configuration of the above described mirrordevice kept in mind.

First Embodiment

The following is a description, in detail, of a mirror device accordingto the present embodiment with reference to the accompanying drawings.

FIGS. 9A through 9C are diagrams exemplifying the configuration of amirror element of a mirror device according to the present embodiment.FIG. 9A is an upper plain view diagram of a mirror element with themirror removed. FIG. 9B is an outline diagram showing a cross-sectionalconfiguration of the mirror element in the cross section B-B′ depictedin FIG. 9A. FIG. 9C is an outline diagram showing a cross-sectionalconfiguration of the mirror element in the cross section A-A′ depictedin FIG. 9A. The mirror element 4001 comprises a mirror 4003, an elastichinge 4007 for supporting the mirror 4003, two address electrodes (i.e.,address electrodes 4008 a and 4008 b) and memory cells (i.e., firstmemory cell 4010 a and second memory cell 4010 b) (not shown in adrawing herein) that correspond to the respective address electrodes.

In the mirror element shown in FIGS. 9A through 9C, the mirror 4003 madeof a high reflective material, such as aluminum and gold, is supportedby the elastic hinge 4007, of which the entirety or a part (e.g., theconnection part with a fixing part, the connection part with a movingpart or the intermediate part) is made of a silicon material, a metallicmaterial or the like, and the mirror 4003 is placed on the devicesubstrate 4004. Here, the silicon material comprehends a poly-silicon,single crystal silicon, amorphous silicon and the like, while themetallic material comprehends aluminum, titanium and an alloy of them.Alternatively, a composite material produced by layering differentmaterials may be used. A ceramic or glass may be used for the elastichinge 4007.

The mirror 4003 is formed as an approximate square, with the length of aside, for example, between 4 μm and 10 μm. Further, the mirror pitch is,for example, between 4 μm and 10 μm. The deflection axis 4005 of themirror 4003 is on the diagonal line thereof.

The light emitted from a light source possessing a coherentcharacteristic is incident to the mirror 4003 from a direction of theorthogonal or diagonal relative to the deflection axis 4005. A lightsource possessing a coherent characteristic is, for example, a laserlight source.

The following is a description of the reason for placing the deflectionaxis of the mirror 4003 on the diagonal line thereof.

FIGS. 10A and 10B are illustrative diagrams showing diffracted lightgenerated when the light is reflected by a mirror of a mirror device.

As shown in the figures, the diffracted light is generated as a resultof irradiating light onto a mirror, and the diffracted light 4110spreads, that is, the primary diffracted light 4111, the secondarydiffracted light 4112, the tertiary diffracted light 4113, and so on, indirections perpendicular to the four sides of the mirror 4003 shown atthe center. In this event, the light intensity decreases gradually withthe primary diffracted light 4111, secondary diffracted light 4112,tertiary diffracted light 4113, and so on. In the case of using a laserlight source, the coherence is improved by the uniformity of thewavelength of a laser light, distinguishing the diffracted light 4110.Note that the diffracted light 4110 also possesses an expansion to thedepth direction of the mirror 4003 in three dimensions.

The mirror device 4000 shown in FIG. 6 can be configured to set thediagonal direction of the mirror 4003 as the deflection axis thereof,thereby making it possible to prevent the diffracted light 4110 of lightfrom entering the projection optical system.

As a result, the diffracted light 4110 does not enter the projectionoptical system and thereby it is possible to improve the contrast of animage to be projected. Further, it is also possible to enhance thecontrast by set the deflecting angle of the mirror 4003 at a large anglerelative to the incidence pupil of the projection lens and also maintainthe numerical aperture of the illumination light at a small value, andthereby the OFF light is separated from the incidence pupil of theprojection lens by a long distance. Such is the reason for placing thedeflection axis of the mirror 4003 on the diagonal line thereof.

The lower end of the elastic hinge 4007 is connected to the devicesubstrate 4004 that includes a circuit for driving the mirror 4003. Theupper end of the elastic hinge 4007 is connected to the bottom surfaceof the mirror 4003. For example, an electrode for securing an electricalcontinuity and an intermediate member for improving the strength of amember and improving the strength of connection may be placed betweenthe elastic hinge 4007 and the device substrate 4004, or between theelastic hinge 4007 and mirror 4003.

Further, a hinge electrode 4009 may be equipped between the elastichinge 4007 and device substrate 4004 as exemplified in FIG. 9C. Notethat a simple notation of “electrode” means the address electrode in thefollowing description.

FIGS. 11A and 11B are diagrams showing an exemplary modification of amirror element of a mirror device according to the present embodiment.FIG. 11A is an upper plain view diagram of the mirror element with themirror removed. FIG. 11B is an outline diagram showing a cross-sectionalconfiguration of the mirror element in the cross section C—C′ depictedin FIG. 11A.

Note that a plurality of elastic hinges (refer to 4007 a and 4007 b) maybe placed along the deflection axis 4005 of the mirror 4003 as shown inFIGS. 11 a and 11 b. Such a placement of elastic hinges is preferablesince the deflecting direction is stabilized, when the mirror isdeflected. Further, when a plurality of elastic hinges is placed asshown in FIGS. 11 a and 11 b, the interval between the plurality ofelastic hinges, or the interval between the plurality of intermediatemembers placed between the hinge and substrate is as large as possible,preferably no less than 30% of the deflection axis length of the mirror.

As exemplified in FIG. 9C, the electrodes 4008 a and 4008 b used fordriving the mirror 4003 are placed on the top surface of the devicesubstrate 4004 and opposite to the bottom surface of the mirror 4003.The form of the address electrodes may be symmetrical or nonsymmetricalabout the deflection axis 4005. The address electrodes are made ofaluminum, tungsten or cupper.The mirror element 4001 further comprises two memory cells, i.e., afirst memory cell 4010 a and a second memory cell 4010 b, for applyingvoltages to the address electrodes 4008 a and 4008 b.

The first and second memory cells 4010 a and 4010 b each has a dynamicrandom access memory (DRAM) structure comprising field effecttransistors (FETs) and a capacitance in this configuration. Thestructures of the individual memory cells 4010 a and 4010 b are notlimited as such and may instead be, for example, a static random accessmemory (SRAM) structure or the like.

Further, the individual memory cells 4010 a and 4010 b are connected tothe respective address electrodes 4008 a and 4008 b, a COLUMN line 1, aCOLUMN line 2 and a ROW line.

In the first memory cell 4010 a, an FET-1 is connected to the addresselectrode 4008 a, COLUMN line 1 and ROW line, respectively, and acapacitance Cap-1 is connected between the address electrode 4008 a andGND (i.e., the ground). Likewise in the second memory cell 4010 b, anFET-2 is connected to the address electrode 4008 b, COLUMN line 2 andROW line, respectively, and a capacitance Cap-2 is connected between theaddress electrode 4008 b and GND.

Controlling the signals on the COLUMN line 1 and ROW line applies apredetermined voltage to the address electrode 4008 a, thereby making itpossible to tilt the mirror 4003 toward the address electrode 4008 a.Likewise, controlling the signals on the COLUMN line 2 and ROW lineapplies a predetermined voltage to the address electrode 4008 b, therebymaking it possible to also tilt the mirror 4003 toward the addresselectrode 4008 b.

Note that a drive circuit for each of the memory cells 4010 a and 4010 bis commonly equipped inside of the device substrate 4004. Thecontrolling of the respective memory cells 4010 a and 4010 b inaccordance with the signal of image data enables control of thedeflection angle of the mirror 4003 and carry out the modulation andreflection of the incident light.

Next is a description of the address electrode comprised in a mirrorelement according to the present embodiment. FIGS. 13A, 13B, 14, 15,16A, 16B, 17, 18A, 18B, 19A, 19B and 20A through 20C are diagrams fordescribing the forms of each respective address electrode comprised inthe mirror element 4001 according to the present embodiment.

In the present embodiment, the address electrode also fills the role ofa stopper for determining the deflection angle of a mirror. Thedeflection angle of a mirror is an angle determined by the apertureratio of a projection lens that satisfies a theoretical resolutiondetermined from the pitch of adjacent mirrors on the basis of the abovedescribed expression:

d=0.61*λ/NA=1.22*λ*F

Alternatively, the deflection angle of a mirror may be set at no lowerangle than the determined angle. Since a laser light possesses a uniformphase, there is more volume of diffracted light than in the lightemitted from a mercury lamp. Therefore, an adverse influence ofdiffracted light can be prevented by setting the deflection angle ofmirror at a larger angle than an appropriate angle approximated from thenumerical aperture NA of the light flux of a laser light source and theF number for a projection lens, and thereby the diffracted light isdifficult to be reflected toward the projection lens. The deflectionangle of mirror is, for example, 10 to 14 degrees, or 2 to 10 degrees,relative to the horizontal state of the mirror 4003. Alternatively, aconfiguration in which the address electrode also fills the role of astopper enables a maximization of a space for placing the electrode whena mirror element is miniaturized as compared to a conventional case inwhich an address electrode and a stopper are provided separately.

Here, what is well known is a phenomenon called “stiction”, that is, amirror 4003 sticks to the contact surface between the mirror 4003 andaddress electrode (i.e., also a stopper) due to a surface tension orintermolecular force when the mirror is deflected. Accordingly, apartial form of the address electrode is configured as a circular arc asshown in FIGS. 13A and 13B so as to make the contact with the mirror4003 a point contact, or as a form to reduce a line contact part asshown in FIG. 14, in order to reduce the occurrence of a stictionphenomenon between the mirror 4003 and address electrode. If the surfaceprecision of the mirror is ill affected as a result of an excessivecontact force, however, the part of the address electrode contactingwith the mirror 4003 is equipped with a slope in the same angle as thetilt angle of the mirror 4003 to adjust the contact pressure as shown inFIG. 15. Note that the address electrode contacts with the mirror 4003face to face in the example shown in FIG. 15. The contact part of theaddress electrode contacting with the mirror 4003 may be a plurality ofplaces as shown in FIGS. 16A and 16B, in lieu of being limited to asingle spot. The configuration as shown in FIGS. 16A and 16B ispreferable because the deflecting direction of the mirror is stablymaintained. In this case, the individual contact points are preferablyplaced apart from each other for no less than 30% of the diagonal sizeof the mirror.

Further, a part of the address electrode including at least the partcontacting with the mirror 4003 may be provided with a passivationlayer, such as halide, in order to reduce the occurrence of a stictionphenomenon between the mirror 4003 and address electrode.

Moreover, an elastic member integrally formed with an address electrodemay be used as stopper.

The form of the address electrode is configured to be a trapezoidconstituted by the top side and bottom side, which are approximatelyparallel to the deflection axis 4005, and by sloped sides approximatelyparallel to the contour line of the mirror 4003 of the mirror device inwhich the deflection axis 4005 of the mirror 4003 is matched with thediagonal line thereof as shown in FIG. 9A. The electrode and stopper arenot individually formed as in the conventional method, and thereforesuch a form is available. Note that the form of the electrode may alsobe configured to divide the above described trapezoid into a pluralitythereof.

Meanwhile, as a configuration for preventing an incidence of undesirablereflection light into the projection light path, at least a part of theelectrode may be covered with a low reflectance material or a thin filmlayer having the film thickness equivalent to ¼ of wavelength λ of thevisible light.

A difference in potentials needs to be generated between the mirror andelectrode for driving the mirror by electrostatic force. The presentembodiment using the electrode also as stopper is configured to providethe surface of the electrode or/and the rear surface of the mirror withan insulation layer(s) in order to prevent an electrical shorting at themirror contacting with the electrode. Further, in the case of providingthe surface of the electrode with an insulation layer, the configurationmay also be such that the insulation layer is provided to only a partincluding the contact part with the mirror. FIG. 9C exemplifies the caseof providing the surface of the address electrode (i.e., addresselectrodes 4008 a and 4008 b) with an insulation layer 4006. Theinsulation layer is made of oxidized compound, azotized compound,silicon or silicon compound, e.g., SiC, SiO₂, Al₂O₃, and Si. Thematerial and thickness of the insulation layer is determined so that thedielectric strength voltage is maintained at no less than the voltagerequired to drive the mirror, most preferably no less than 5 volts. Forexample, the dielectric strength voltage may be configured to be twotimes the drive voltage of the mirror or higher, 3 volts or higher or 10volts or higher. Further, a selection of an insulation material so as topossess a resistance to an etchant in the production process makes itpossible to also function as electrode protective film in the process ofetching a sacrifice layer in the production process (which is describedin detail later), thereby simplifying the production process, which ispreferable.

Next is a description of one example related to the size and form of anaddress electrode.

Referring to FIG. 17, where “L1” is the distance between the deflectionaxis and the edge of the electrode on a side closer to the deflectionaxis of the mirror 4003, “L2” is the distance between the deflectionaxis and the edge of the electrode on a side far from the deflectionaxis of the mirror 4003, and “d1” and “d2” are the distance between themirror bottom surface and electrode at the respective edges. Now for adescription, “P1” is a representative point at the electrode edge on theside closer to the deflection axis of the mirror and “P2” is arepresentative point at the electrode edge on the side far from thedeflection axis of the mirror.

The example shown in FIG. 17 is the case in which the electrode isformed so as to constitute: d1<d2. In this configuration, the stopperdetermining the tilt angle of the mirror 4003 is preferred to be placedat the point P2 in consideration of a production variance of theelectrode height that influences the deflection angle of the mirror. Thepresent embodiment is accordingly configured to satisfy the relationshipof:

d1>(L1*d2)/L2

This configuration provides a good usage efficiency of the space underthe mirror and maintains a stable deflection angle of the mirror.

Note that, while the example shown in FIG. 17 forms between the pointsP1 and P2 in a continuous slope; alternatively, a stepwise electrode maybe formed as shown in FIGS. 18A and 18B for easing the production.Further, it is not only possible to form an electrode so that thedeflection angle of the mirror 4003, when it contacts with an addresselectrode on one side, and the deflection angle of the mirror 4003, whenit contacts with the address electrode on the other side, are the sameas shown in FIG. 19A, or different from each other as shown in FIG. 19B.That is, it is possible to configure the address electrode such that,for example, the deflection angle in the OFF state is larger than thatin the ON state.

Meanwhile, when considering an occurrence of stiction between theaddress electrode and mirror, it is possible to state that the closerthe contact point to the deflection axis, the more advantageous it isbecause the moment impeding the motion of the mirror due to the stictionis smaller. FIGS. 20A, 20B and 20C exemplify the case of forming thestoppers at a site other than the farthest site from the deflection axisof the external forms that forms the address electrode. If there isstill a concern on an occurrence of stiction even if an addresselectrode is provided with a coating layer for preventing stiction, theconfigurations as shown in FIGS. 20A, 20B and 20C are viable.

Further, in the case of configuring the electrode to constitute d1=d2,the point on the electrode determining the deflection angle of themirror is P2 and the configuration is determined so as to satisfy thefollowing expression:

cot θ=d2/L2

Next is an outline description of the circuit comprisal of the mirrordevice according to the present embodiment.

As exemplified in FIG. 21, the mirror device 4000 according to thepresent embodiment comprises a mirror element array 5110, COLUMN drivers5120, ROW line decoders 5130 and an external interface unit 5140.

The external interface unit 5140 comprises a timing controller 5141 anda selector 5142. The timing controller 5141 controls the row linedecoder 5130 on the basis of a timing signal from an SLM controller (noshown in a drawing here). The selector 5142 supplies the column driver5120 with digital signal incoming from the SLM controller.

In the mirror element array 5110, a plurality of mirror elements 4001 isarrayed at the positions where individual bit lines, which arevertically extended respectively from the column drivers 5120, crossesindividual word lines which are horizontally extended respectively fromthe row decoders 5130.

In each mirror element 4001, electrical potentials are applied to theaddress electrodes 4008 (i.e., the address electrodes 4008 a and 4008 b)by way of the memory cells (i.e., the first memory cell 4010 a and thesecond memory cell 4010 b), which are exemplified in FIG. 12, on thebasis of signals from the bit lines and word line. Here, the bit linescorrespond to the COLUMN lines 1 and 2, which are shown in FIG. 12, andthe word line corresponds to the ROW line shown in FIG. 12. In themeantime, the address electrodes 4008 a and 4008 b are noted as OFFelectrode 5116 and ON electrode 5115, respectively, in the followingdescription for convenience.

Incidentally, as another method of a mirror drive for displaying animage in higher grade of gradations with a reduced drive voltage, thereis a technique disclosed in US Patent Application 20050190429. In thisdisclosure, a mirror is put to a free oscillation in the inherentoscillation frequency, and thereby the intensity of light that is about25% to 37% of the emission light intensity produced when a mirror iscontrolled under a constant ON can be obtained during the oscillationperiod of the mirror. According to such a control, there is noparticular need to drive the mirror in high speed, making it possible toobtain a high level of gradations with a low spring constant of a springmember supporting the mirror, and therefore enabling a reduction in thedrive voltage. Furthermore, a combination with the method of decreasingthe drive voltage by decreasing the deflection angle of a mirror asdescribed above brings forth a greater deal of effect.

According to the present embodiment, the use of a laser light sourcemakes it possible to decrease the deflection angle of a mirror and alsominiaturize the mirror device without ushering in a degradation ofbrightness, and further, the use of the above described oscillationcontrol enables a higher level of gradations without causing an increasein the drive voltage.

FIG. 22A is a diagram depicting a state in which an incident light isreflected toward a projection optical system by deflecting the mirror ofa mirror element. Note that this case exemplifies the case ofdesignating the deflection angle at 13 degrees, a deflection angle,however, is not limited as such.

Giving a signal (0, 1) to the memory cells 4010 a and 4010 b (which arenot shown here) described in FIG. 12 applies a voltage of “0” volts tothe address electrode 4008 a of FIG. 22A and applies a voltage of Vavolts to the address electrode 4008 b. As a result, the mirror 4003 isdeflected from a deflection angle of “0” degrees, i.e., the horizontalstate, to that of +13 degrees attracted by a coulomb force in thedirection of the address electrode 4008 b to which the voltage of Vavolts is applied. This causes the incident light to be reflected by themirror 4003 toward the projection optical system (which is called the ONstate).

Note that the present specification document defines the deflectionangles of the mirror 4003 as “+” (positive) for clockwise (CW) directionand “−” (negative) for counterclockwise (CCW) direction, with “0”degrees as the initial state of the mirror 4003. Further, an insulationlayer 4006 is provided on the device substrate 4004 and a hingeelectrode 4009 connected to the elastic hinge 4007 is grounded throughthe insulation layer 4006.

FIG. 22B is a diagram depicting a state in which an incident light isreflected not toward a projection optical system by deflecting themirror of a mirror element. Giving a signal (1, 0) to the memory cells4010 a and 4010 b (which are not shown here) described in FIG. 12applies a voltage of Va volts to the address electrode 4008 a, and “0”volts to the address electrode 4008 b. As a result, the mirror 4003 isdeflected from a deflection angle of “0” degrees, i.e., the horizontalstate, to that of −13 degrees attracted by a coulomb force in thedirection of the address electrode 4008 a to which the voltage of Vavolts is applied. This causes the incident light to be reflected by themirror 4003 to elsewhere other than the light path toward the projectionoptical system (which is called the OFF state).

FIG. 22C is a diagram delineating a state in which reflecting and notreflecting an incident light toward a projection optical system arerepeated by free-oscillating the mirror of a mirror element.

In either of the states shown in FIGS. 22A and 22B, in which the mirror4003 is pre-deflected, the giving of a signal (0, 0) to the memory cells4010 a and 4010 b (which are not shown here) applies a voltage of “0”volts to the address electrodes 4008 a and 4008 b. As a result, thecoulomb force, which has been generated between the mirror 4003 and theaddress electrode 4008 a or 4008 b, is eliminated so that the mirror4003 performs a free oscillation within the range of the deflectionangles ±13 degrees in accordance with the property of the elastic hinge4007. Associated with the free oscillation of the mirror 4003, theincident light is reflected toward the projection optical system foronly within the range of a specific deflection angle. The mirror 4003repeats the free oscillations, changing over frequently between the ONlight state and OFF light state. Controlling the number of changeoversmakes it possible to finely adjust the intensity of light reflectedtoward the projection optical system (which is called a free oscillationstate).

The total intensity of light reflected by means of the free oscillationtoward the projection optical system is certainly lower than theintensity that is produced when the mirror 4003 is continuously in theON state and higher than the intensity that is when it is continuouslyin the OFF state. That is, it is possible to make an intermediateintensity between those of the ON state and OFF state. Therefore, ahigher gradation image can be projected than with the conventionaltechnique by finely adjusting the intensity as described above.

Although not shown in the drawing, an alternative configuration may besuch that only a portion of light is made to enter the projectionoptical system by reflecting an incident light in the initial state of amirror 4003. Configuring as such makes a reflection light enter theprojection optical system in higher intensity than that produced whenthe mirror 4003 is continuously in the OFF light state and lowerintensity than that produced when the mirror 4003 is continuously in theON light state (which is called an intermediate state).

FIG. 23 is a chart showing the transition response between the ON stateand OFF state of the mirror 4003. In a transition from the OFF state inwhich the mirror 4003 is abutted on the address electrode 4008 a bybeing attracted thereby to the ON state in which the mirror 4003 isabutted on the address electrode 4008 b by being attracted thereby, arise time t_(r) is required before the mirror 4003 becomes a complete ONstate in the early stage of starting the transition; and in a transitionfrom the ON state to OFF state, a fall time t_(f) is likewise requiredbefore the mirror becomes a complete OFF state. Note that the followingdescription calls the rise time t_(r) and fall time t_(f) integrally asa mirror changeover transition time t_(M) when they are notdistinguished.

Next is an outline description of the inherent frequency of theoscillation system of a mirror device according to the presentembodiment.

The fact that a drive voltage can be lowered by obtaining a finegradation by means of a free oscillation of a mirror is alreadydescribed above. Now, if an LSB light intensity by way of a common PWMdrive is intended to be obtained by an oscillation, the naturaloscillation cycle of an oscillation system that includes an elastichinge is designated as follows:

The natural oscillation cycle T of an oscillation system=2*π*√(I/K)=LSBtime/X[%];

where:I: the moment of rotation of an oscillation system,K: the spring constant of an elastic hinge,LSB time: the LSB cycle at displaying n bits, andX [%]: the ratio of the light intensity obtained by one oscillationcycle to the Full-ON light intensity of the same cycleNote that:“I” is determined by the weight of a mirror and the distance between thecenter of gravity and the center of rotation;“K” is determined on the basis of the thickness, width, length andcross-sectional shape of an elastic hinge;“LSB time” is determined from on the basis of frame time, or one frametime and the number of reproduction bits in the case of a single-panelprojection method;“X” is determined particularly on the basis of the F number of aprojection lens and the intensity distribution of an illumination light.

As an example, when a single-panel color sequential method is employed,the ratio of emission intensity by one oscillation is assumed to be 32%and the minimum emission intensity in a 10-bit grayscale is desired tobe obtained by an oscillation, then “I” and “K” are designed so as tohave a natural oscillation cycle as follows:

T=1/(60*3*2¹⁰*0.32)≈17.0 μsec.

In contrast, when a conventional PWM control is employed to make thechangeover transition time t_(M) of a mirror approximately equal to thenatural oscillation frequency of the oscillation system of the mirrorand also the LSB is regulated so that a shortage of the light intensityin the interim can be sufficiently ignored, the gray scale reproduciblewith the above described hinge is about 8-bit even if the LSB is set atfive times the changeover transition time t_(M). That is, it iscomprehensible that a 10-bit grayscale can be reproduced by using theelastic hinge that would have made it possible to reproduce about an8-bit grayscale according to the conventional control.

In a single-panel projection apparatus, an example configurationattempting to obtain, for example, 13-bit grayscale is as follows:

LSB time=(1/60)*(1/3)*(1/2¹³)=0.68 μsec

If a configuration is such that the light intensity obtained in onecycle for the optical comprisal is 38% of the intensity of the casecontrolling a mirror under a constant ON for the same cycle, theoscillation cycle T is as follows:

T=0.68/0.38%=1.8 μsec

In contrast, when an 8-bit grayscale is attempted to be obtained in themulti-panel projection apparatus, an example comprisal is as follows:

LSB time=(1/60)*(1/3)*(1/2⁸)=21.7 μsec

If a configuration is such that the light intensity obtained in onecycle for the optical comprisal is 20% of the case controlling a mirrorunder a constant ON for the same cycle, the oscillation cycle T is asfollows:

T=65.1/20%=108.5 μsec.

As described above, the present embodiment is configured to set thenatural oscillation cycle of the oscillation system, which includes anelastic hinge, between about 1.8 μsec and 110 μsec; and to use threedeflection state, i.e., a first deflection state (ON state), in whichthe light modulated by the mirror element is headed to the projectionlight path, a second deflection state (OFF state), in which the light isheaded to elsewhere other than the projection light path, and a thirddeflection state (oscillation state), in which the mirror oscillatesbetween the first and second deflection states, thereby enabling thedisplay of a high gradation image without requiring an increase in thedrive voltage of the mirror element.

FIG. 24A shows a cross-section of a mirror element that is configured tobe equipped with only one address electrode and one drive circuit asanother embodiment of a mirror element.

The mirror element 4011 shown in FIG. 24A is equipped with an insulationlayer 4006 on a device substrate 4004 including one drive circuit fordeflecting a mirror 4003. Further, an elastic hinge 4007 is equipped onthe insulation layer 4006. The elastic hinge 4007 supports one mirror4003, and one address electrode 4013, which is connected to the drivecircuit, is equipped under the mirror 4003. Note that the area sizes ofthe address electrode 4013 exposed above the device substrate 4004 areconfigured to be different between the left side and right side of theelastic hinge 4007, or the deflection axis of mirror 4003, with the areasize of the exposed part of the address electrode 4013 on the left sideof the elastic hinge 4007 being larger than the area size on the rightside, in FIG. 24A.

Here, the mirror 4003 is deflected by the electrical control of oneaddress electrode 4013 and drive circuit. Further, the deflected mirror4003 is retained at a specific deflection angle by contacting withstopper 4012 a or 4012 b, which are equipped in the vicinity of theexposed parts on the left and right sides of the address electrode 4013.

Note that, here, an alternative configuration may be such as toeliminate the stopper for securing the area for the electrode asdescribed above and cause the mirror to abut the address electrodedirectly.

Further, a hinge electrode 4009 connected to the elastic hinge 4007 isgrounded through the insulation layer 4006. Such is the comprisal of themirror element 4011.

Incidentally, the present specification document calls the part, whichis exposed above the device substrate 4004, of the address electrode4013 of FIG. 24A as electrode part, in specific, calls the left part as“first electrode part” and the right part as “second electrode part,with the elastic hinge 4007 or the deflection axis of mirror 4003referred to as the border.

As such, the applying of a voltage by configuring the address electrode4013 to be asymmetrical, that is, the left side is different from theright side, e.g., the area sizes, in relation to the elastic hinge 4007or the deflection axis of mirror 4003 generates the difference incoulomb force between (a) and (b), where (a): a coulomb force generatedbetween the first electrode part and mirror 4003, and (b): a coulombforce generated between the second electrode part and mirror 4003. Themirror 4003 can be deflected by differentiating the coulomb forcebetween the left and right sides of the deflection axis of the elastichinge 4007 or mirror 4003.

Meanwhile, FIG. 24B is an outline diagram of a cross-section of themirror element 4011 shown in FIG. 24A.

Requiring only one address electrode 4013 makes it possible to reducethe two memory cells 4010 a and 4010 b, which correspond to the twoaddress electrodes 4008 a and 4008 b in the configuration of FIG. 12, toone memory cell 4014. This in turn makes it possible to reduce thenumber of wirings for controlling the deflection of the mirror 4003.

Other comprisals are similar to the configuration described for FIG. 12and therefore the description is not provided here.

Next is a description, in detail, of a single address electrode 4013controlling the deflection of a mirror with reference to FIGS. 25A, 25Band 25C, and FIG. 26.

Mirror elements 4011 a and 4011 b respectively shown in FIGS. 25A and25B each is configured such that the respective area sizes of the firstand second electrode parts of one address electrode 4013 on the left andright sides, sandwiching the deflection axis 4015 of the mirror 4003,are different from each other (i.e., asymmetrical).

FIG. 25A shows a plain view diagram; and a cross-sectional diagram, bothof a mirror element 4011 a structured such that the area size S1 of afirst electrode part of one address electrode 4013 a and the area sizeS2 of a second electrode part thereof are in the relationship of S1>S2,and such that the connection part between the first and second electrodeparts exists in the same structural layer as the layer in which thefirst and second electrode parts exist.

In contrast, FIG. 25B shows a plain view diagram, and a cross-sectionaldiagram, both of a mirror element 4011 b structured such that the areasize S1 of a first electrode part of one address electrode 4013 b andthe area size S2 of a second electrode part thereof are in therelationship of S1>S2, and such that the connection part between thefirst and second electrode parts exists in a structural layer differentfrom the layer in which the first and second electrode parts exist.

Next is a description of the control for the deflecting operation of amirror in the mirror element 4011 a or 4011 b, each respectively shownin FIG. 25A or 25B.

FIG. 26 is a diagram showing a data input to the mirror elements 4011 aor 4011 b, the voltage application to the address electrodes 4013 a or4013 b, and the deflection angles of the mirror 4003, in a time series.

Referring to FIG. 26, the “data input” is to the mirror element 4011 aor 4011 b, which is controlled in two states, i.e., HI and LOW, with theHI representing a data input, that is, projecting an image and LOWrepresenting no data input, that is, not projecting an image.

The following description refers to the control of only the mirrorelement 4011 a shown in FIG. 25A, of the two mirror element 4011 a andmirror element 4011 b (which is shown in FIG. 25B), unless otherwisenoted.

Next, the vertical axis of the “address voltage” of FIG. 26 representsthe voltage values applied to the address electrode 4013 a of the mirrorelement 4011 a, and the voltage values applied to the address electrode4013 a is, for example, “4” volts and “0” volts.

The vertical axis of the “mirror angle” of FIG. 26 represents thedeflection angle of the mirror 4003, defining the deflection angle ofthe mirror 4003 in the state in which it is parallel to the devicesubstrate 4004 to be “0” degrees. Further, with the first electrode partof the address electrode 4013 a defined as the ON state side, themaximum deflection angle of the mirror 4003 in the ON state is set at−13 degrees. On the other hand, with the second electrode part of theaddress electrode 4013 a defined as the OFF state side, the maximumdeflection angle of the mirror 4003 in the OFF state is set at +13degrees. Therefore, the mirror 4003 deflects within a range in which themaximum deflection angles of the ON state and OFF state are ±13.

Note that the deflection angle is designated at 13 degrees as an examplehere; the deflection angle is not limited as such.

Further, the horizontal axis of FIG. 26 represents elapsed time t.

When the deflecting operation of the mirror 4003 is performed in theconfiguration of FIG. 25A, a voltage is applied to the address electrode4013 a at the timing on the basis of the passage of time due to a datainput and a data rewrite.

Referring to FIG. 26, no data is input between the time t0 and t1, andthe mirror 4003 is accordingly in the initial state. That is, thedeflection angle of the mirror 4003 is “0” degrees in the state, inwhich no voltage is applied to the address electrode 4013 a.

At the time t1, a voltage of 4 volts is applied to the address electrode4013 a, causing the mirror 4003 to be attracted by a coulomb forcegenerated between the mirror 4003 and address electrode 4013 a towardthe first electrode part having a large area size so that the mirror4003 shifts from the 0-degree deflection angle at the time t1 to a−13-degree deflection angle at the time t2.

Then the mirror 4003 is retained onto the stopper 4012 a of the firstelectrode part side or onto the first electrode part.

The distance G1 between the mirror 4003 and the first electrode part andthe distance G2 between the mirror 4003 and the second electrode part,both when the mirror 4003 is in the initial state, are the same, and thefirst electrode part has a larger area than the second electrode partdoes, and therefore the first electrode part can retain a larger amountof charge. As a result, a larger coulomb force is generated for thefirst electrode part. The mirror 4003 is retained onto the stopper 4012a of the first electrode part side or onto the first electrode part as aresult of continuously applying a voltage of 4 volts to the addresselectrode 4013 a in accordance with a period on the basis of a datainput between the time t2 and time t3.

Then, at the time t3, stopping the data input applies a voltage of “0”volts to the address electrode 4013 a. As a result, the coulomb forcegenerated between the address electrode 4013 a and mirror 4003 iscancelled. This causes the mirror 4003 retained on the first electrodepart side to be shifted to a free oscillation due to the restoring forceof the elastic hinge 4007.

Further, the deflection angle of the mirror 4003 becomes θ>0 degrees,and when a voltage of 4 volts is applied to the address electrode 4013 aat the time t4 when a coulomb force F1, which is generated between themirror 4003 and first electrode part, and a coulomb force F2, which isgenerated between the mirror 4003 and second electrode part, constitutesthe relationship of F1<F2, and thereby the mirror 4003 is attracted tothe second electrode part.

Then at the time t5, the mirror 4003 is retained onto the stopper 4012 bof the second electrode part or onto the second electrode part.

The reason is that the second power of a distance has a larger effect ona coulomb force F than the difference in electrical potentials does,according to the expression.

Therefore, with an appropriate adjustment of the area sizes of the firstand second electrode parts, a coulomb force F acts more strongly to thesmaller distance G2 of the distance between the address electrode 4013 aand mirror 4003, despite that the area S2 of the second electrode partis smaller than the area S1 of the first electrode part. As a result,the mirror 4003 can be deflected to the second electrode part.

Note that the transition time of the mirror 4003 between the time t3 andt4 is preferred to be performed in about 4.5 μsec in order to obtain ahigh grade of gradation. Further, a control can possibly be performed insuch a manner to turn off the illumination light synchronously with atransition of the mirror 4003 so as to not let the illumination light bereflected and incident to the projection light path during a datarewrite, that is, during the transition of the mirror 4003, between thetime t3 and t4.

Between the time t5 and t6, the mirror 4003 is continuously retainedonto the stopper 4012 b of the second electrode part or onto the secondelectrode part by keeping applying the voltage to the address electrode4013 a.

In this event, no data is input and therefore no image is projected.

Then, at the time t6, a new data input is carried out. The voltage of 4volts, which has been applied to the address electrode 4013 a, ischanged over to “0” volts at the time t6 in accordance with the datainput. This operation cancels the coulomb force generated between themirror 4003 retained onto the second electrode part and the addresselectrode 4013 a likewise the case of the time t3 so that the mirror4003 shifts to a free oscillation state due to the restoring force ofthe elastic hinge 4007.

Further, a voltage of 4 volts is again applied to the address electrode4013 a at the time t7 when a coulomb force F1, which is generatedbetween the mirror 4003 and first electrode part, and a coulomb forceF2, which is generated between the mirror 4003 and second electrodepart, constitutes the relationship of F1>F2 when the deflection angle ofthe mirror 4003 becomes θ<0 degrees, and thereby the mirror 4003 isattracted to the first electrode part, and then the mirror 4003 isretained onto the first electrode part at the time t8.

This principle is understood from the description of the action of acoulomb force between the above described time t3 and t5. Also in thisevent, the transition time of the mirror 4003 between the time t6 and t7is preferred to be performed in about 4.5 μsec, and the control isperformed in such a manner to turn off the illumination lightsynchronously with a transition of the mirror 4003 so as to not let theillumination light be reflected and incident to the projection lightpath during the transition of the mirror 4003.

Then, between the time t8 and t9, the mirror 4003 is continuouslyretained onto the stopper 4012 a of the first electrode part or onto thefirst electrode part by keeping applying a voltage of 4 volts to theaddress electrode 4013 a.

In this event, data is continuously input and images are projected.

Then, the voltage applied to the address electrode 4013 a is changedfrom 4 volts to “0” volts as the data input is stopped at the time t9.This operation puts the mirror 4003 into the free oscillation state.

Then, applying a voltage to the address electrode 4013 a at the time t10makes it possible to retain the mirror 4003 onto the stopper 4012 b ofthe second electrode part or onto the second electrode part at the timet11 on the same principle as that applied between the time t3 and t5 andbetween the time t6 and t8.

A repetition of the similar operation enables the control for deflectingthe mirror 4003.

Next is a description of a control for returning the mirror 4003, whichis retained onto the stopper 4012 a of the first electrode part or ontothe first electrode part, or onto the stopper 4012 b of the secondelectrode part or onto the second electrode part, back to the initialstate.

In order to return the mirror 4003 from the state, in which a voltage isapplied to the address electrode 4013 a and so the mirror 4003 isretained onto the stopper 4012 a of the first electrode part side oronto the first electrode part, or onto the stopper 4012 b of the secondelectrode part or onto the second electrode part, back to the initialstate, an appropriate pulse voltage is to be applied.

For example, in a state in which the mirror 4003 is retained onto thestopper 4012 a on the first electrode part side or onto the firstelectrode part, or retained onto the stopper 4012 b on the secondelectrode part side or onto the second electrode part, the changing ofthe voltages applied to the address electrode 4013 a to “0” volts causesthe mirror 4003 to perform a free oscillation. When the distance betweenthe address electrode 4013 a and mirror 4003 becomes appropriate in themidst of the mirror 4003 heading from the first electrode part side tothe second electrode part side, or vice versa, in the state in which themirror 4003 is performing the free oscillation, a temporary applicationof an appropriate voltage to the address electrode 4013 a generates acoulomb force F that pulls the mirror 4003 back to the first electrodepart or second electrode part, to which the mirror has been retained,that is, generates acceleration in a direction opposite to the directionof the mirror 4003 heading, and thereby the mirror 4003 can be returnedto the initial state.The application of a pulse voltage to one address electrode 4013 a asdescribed above makes it possible to carry out a control for returningthe mirror 4003 from a state in which it is retained onto the stopper4012 a on the first electrode part side or onto the first electrodepart, or retained onto the stopper 4012 b on the second electrode partside or onto the second electrode part, to the initial state.

Considering the principle of the coulomb force between the mirror andaddress electrode 4013 a as described above, the applying of a voltageto the address electrode 4013 a at an appropriate distance between themirror 4003 and address electrode 4013 a also makes it possible toretain the mirror 4003 at the deflection angle of the OFF state byreturning the mirror 4003 from the ON state, or at the deflection angleof the ON state by returning the mirror 4003 from the OFF state.

The above description is the same in the case of the address electrode4013 b of the mirror element 4011 b shown in FIG. 25B.

Note that the control of the mirror 4003 of the mirror elements 4011 aand 4011 b shown in FIG. 26 is widely applicable to a mirror elementthat is configured to have a single address electrode and to beasymmetrical about the elastic hinge or the deflection axis of mirror.

As described above, the mirror can be deflected to the deflection angleof the ON state or OFF state, or put in the free oscillation state, witha single address electrode of a mirror element.

FIG. 25C shows a plain view diagram, and a cross-sectional diagram, bothof a mirror element 4011 c structured such that the area size S1 of afirst electrode part of one address electrode and the area size S2 of asecond electrode part thereof are in the relationship of S1=S2, and suchthat the distance G1 between a mirror 4003 and the first electrode partand the distance G2 between the mirror 4003 and the second electrodepart are in the relationship of G1<G2.

That is, the configuration of FIG. 25C is such that, for the addresselectrode 4013 c, the height of the first electrode part is differentfrom that of the second electrode part and such that the distance G1between the first electrode part and mirror 4003 and the distance G2between the second electrode part and mirror 4003 is in the relationshipof G1<G2. It is further such that the address electrode 4013 c iselectrically connected to the first electrode part and second electrodepart on the same layer as the address electrode 4013 c exists.

In the case of the mirror element 4011 c as shown in FIG. 25C, the sizeof the coulomb force generated between the mirror 4003 and addresselectrode 4013 c in the first electrode part is different from thatgenerated between the mirror 4003 and address electrode 4013 c in thesecond electrode part because the distances between the mirror 4003 andaddress electrode 4013 c are different in the first electrode part andthe second electrode part. Therefore, the deflection of the mirror 4003can be controlled by carrying out a control similar to the case of theabove described FIG. 26.

Note that the deflection angle of the mirror 4003 is retained by usingthe stoppers 4012 a and 4012 b in FIGS. 25A, 25B and 25C, the deflectionangle of the mirror 4003, however, can be established by configuring anappropriate height of the address electrode 4013 c to also fill theroles of the stoppers 4012 a and 4012 b.

Further, while the present embodiment is configured to set the controlvoltages at 4-volt and 0-volt applied to the address electrode 4013 a,4013 b or 4013 c, such control voltages, however, are arbitrary andother appropriate voltages may be used to control the mirror 4003.

Furthermore, the mirror can be controlled with multi-step voltages to beapplied to the address electrode 4013 a, 4013 b or 4013 c. As anexample, if the distance between the mirror 4003 and address electrode4013 a, 4013 b or 4013 c is short, increasing a coulomb force, themirror 4003 can be controlled with a lower voltage than that when themirror 4003 is in the initial state.

As described above, even with the configuration in which each mirrorelement comprises only one address electrode, the using of threedeflection states, i.e. the first deflection state (i.e., the ON state)in which the light modulated by the mirror element is headed toward aprojection light path, the second deflection state (i.e., the OFF state)in which the deflected light is headed elsewhere other than theprojection light path and the third deflection state (i.e., theoscillation state) in which the mirror element oscillates between thefirst and second deflection states, makes it possible to display animage with a high grade of gradations without requiring an increase inthe drive voltage for the mirror element.

As such, each mirror element of the mirror device according to thepresent embodiment is configured to change the deflection states of themirror in accordance with the voltage applied to the electrode,deflecting the light incident to the mirror 4003 to specific directionsas shown in FIG. 27 as an example.

Note that FIG. 27 is an illustrative cross-sectional diagram depicting asituation of reflecting a light flux of the F number 10 (f/10) emittedfrom a laser light source possessing a coherent characteristic for amirror device configured such that the deflection angles of the mirrorin ON light state and OFF light state are designated as ±3 degrees,respectively. The illumination light ejected from the light source 4002is incident to the mirror 4003 as depicted by an optical axis 4121.Then, the illumination light is reflected as depicted by an optical axis4122 in the ON state of the mirror 4003, is reflected as depicted by anoptical axis 4124 in the OFF state of the mirror 4003 and is reflectedas depicted by an optical axis 4123 in the initial state of the mirror4003. The configuring as such makes it possible to not allow moresecurely the diffraction light and scattered light generated by themirror in the OFF light state or OFF angle to enter a projection opticalsystem 4125.

Next is an outline description of a package used for a mirror deviceaccording to the present embodiment.

FIGS. 28A and 28B are diagrams exemplify the configuration of anassembly body that packages two mirror devices. The assembly body 2400comprises a cover glass 2010 and a package substrate 2004 which made ofglass, silicon, ceramics, metal or a composite body constituted by someof these materials. Glass used for the package substrate 2004 ispreferred to use a material with high thermal conductivity, i.e., sodaash glass (0.55 to 0.75 W/mK) and Pyrex glass (1 W/mK) for improvingradiation efficiency. The assembly body 2400 may comprise a thermalconductive member and a cooling/radiation member 2013 aiming atradiation. The materials for these package constituent members areselected in such a manner as to have inherently similar values ofthermal expansion coefficients as much as possible, thus preventing afailure, such as crack, mutual pealing off, from occurring in the actualusage environment.

Further, an intermediate member 2009 for joining the individualconstituent members comprises a support part 2007 for determining theheight of the cover glass 2010, and a joinder member made of frittedglass, solder, epoxy resin, or the like. The cover glass may further beprovided with a light shield layer 2006 for shielding extraneous lightand an anti-reflection (AR) coating 2011 for preventing an extraneousreflection of the incident light. The anti-reflection coating 2011 is acoating made of magnesium fluoride or a nanostructure forming of no morethan the wavelength applied to a glass surface. The light shield layer2006 is constituted by a black thin film layer containing carbon, or amultilayer structure consisting of a black thin film layer and ametallic layer.

Note that it is possible to accommodate a plurality of mirror devicesand a control circuit 2017 inside of the package shown in FIG. 28A.The accommodating of a plurality of devices in one package conceivablyincludes various benefits in addition to a cost reduction. In aprojection apparatus comprising the assembly body 2400, the projectingposition of each device is basically adjusted by the positionaladjustment of the respective optical elements and so the pixels of theindividual mirror devices 2030 and 2040 are overlapped with each otherin good accuracy and therefore a reduction in the resolution of theprojected image is small. Furthermore, the colors reflected by therespective mirror devices 2030 and 2040 are observed with little blur.Note that FIGS. 28A and 28B exemplify a configuration in which a mirrorarray 2032 is placed on a device substrate 2031 and a mirror array 2042is places on a device substrate 2041.Further, equipping the control circuit 2017 inside of the package asexemplified in FIGS. 28A and 28B enables one package substrate toaccommodate a very large number of circuit wirings pattern 2005 of thecontrol circuit 2017. As a result, the floating capacity of the circuitwirings pattern 2005, et cetera, are substantially reduced. Furthermore,it is possible to place the control circuit 2017 controlled in higherspeed than a video image signal at a position equidistance from theindividual mirror devices 2030 and 2040, respectively, so thedifferences in resistance values and floating capacitance values betweenthe respective circuit wirings pattern 2005 connected to the individualmirror devices 2030 and 2040 are reduced. This accordingly makes itpossible to use a mirror device with a large number of mirror elementsand a mirror device allowing a large volume of data processing volume inhigh degree of gradation. This in turn enables a projection of an imagein high degrees of gradation and resolution. Further, the shortening ofthe circuit wiring from the control circuit 2017 to each mirror devicemakes it easy to synchronize the timings, between the individual mirrordevices, for controlling the respective mirror devices in high speed.Further, the thermal environment conditions of a plurality of mirrordevices placed on the same package substrate become the same, andthereby the shifts in the positions of the mirror elements of theindividual mirror devices due to thermal expansion turn to be the same.Therefore the projection states can be made identical. Further, thecontrols for the individual mirror devices can be handled as the sameenvironment, so an analogous control for the mirrors and the controlcondition of the voltage value for the memory can be made the same.Furthermore, a projection apparatus 2500 shown in FIGS. 29A through 29Dis configured such that the prism members and cover glass of theassembly body, which packages the above described plurality of mirrordevices, with thermal conductive members 2062. This enables an exchangeof heat between the prisms and mirror devices, making it possible toradiate heat in a lump by way of radiation means (not shown in a drawingherein) equipped on the mirror device or prism member. The projectionapparatus 2500 shown in FIGS. 29A through 29D is described later indetail.Note that the mirror devices 2030 and 2040 and the device substrates2031 and 2041, which are shown in FIGS. 28A through 29D, correspond tothe mirror device 4000 and device substrate 4004, respectively, whichare shown in FIG. 6; and the mirror arrays 2032 and 2042 shown in FIGS.28A through 29D correspond to the mirror element array 5110 shown inFIG. 21.As described above, the mirror device according to the presentembodiment is configured such that the electrode also fills the role ofa stopper for regulating the deflection angle of a mirror and thereby aspace utilization efficiency is improved when a mirror element isminiaturized, enabling an increase in the area size of the electrode.Therefore, a parallel application of an oscillation control for a mirrormakes it possible to enable both a miniaturization of the mirror deviceand an enhancement of gradations.Note that the mirror pitch, mirror gap, deflection angle and drivevoltage of the mirror device according to the present embodiment are notlimited to the values exemplified in the above description and ratherpreferably in the following ranges (respective both ends inclusive): themirror pitch is between 4 μm and 10 μm; the mirror gap is between 0.15μm and 0.55 μm; the maximum deflection angle of mirror is between 2degrees and 14 degrees; and the drive voltage of mirror is between 3volts and 15 volts.

Second Embodiment

With reference to the accompanying drawings, the following is adescription of a projection apparatus according to the presentembodiment comprising a mirror device described in detail for the firstembodiment.

First is a description of the configuration of a single-panel projectionapparatus comprising a single spatial light modulator and displaying acolor display with the frequencies of projected light changed in a timeseries, with reference to FIG. 30.Note that the spatial light modulated used in the present embodiment isactually the mirror device 4000 described in detail for the firstembodiment.FIG. 30 is a conceptual diagram showing the configuration of asingle-panel projection apparatus according to the present embodiment.A projection apparatus 5010 comprises a single spatial light modulator(SLM) 5100, a control unit 5500, a Total Internal Reflection (TIR) prism5300, a projection optical system 5400 and a light source optical system5200 as exemplified in FIG. 30.

The projection optical system 5400 is equipped with the spatial lightmodulator 5100 and TIR prism 5300 in the optical axis of the projectionoptical system 5400, and the light source optical system 5200 isequipped in such a manner that the optical axis thereof matches that ofthe projection optical system 5400.

The TIR prism 5300 fills the function of making an illumination light5600, which is incoming from the light source optical system 5200 placedonto the side, enter the spatial light modulator 5100 at a prescribedinclination angle relative thereto as incident light 5601 and making areflection light 5602 reflected by the spatial light modulator 5100transmit so as to reach the projection optical system 5400.

The projection optical system 5400 projects the reflection light 5602incoming by way of the spatial light modulator 5100 and TIR prism 5300to a screen 5900 and such, as projection light 5603.

The light source optical system 5200 comprises a variable light source5210 for generating the illumination light 5600, a condenser lens 5220for focusing the illumination light 5600, a rod type condenser body 5230and a condenser lens 5240.

The variable light source 5210, condenser lens 5220, rod type condenserbody 5230 and condenser lens 5240 are sequentially placed in theaforementioned order in the optical axis of the illumination light 5600emitted from the variable light source 5210 and incident to the sideface of the TIR prism 5300.

The projection apparatus 5010 employs a single spatial light modulator5100 for implementing a color display on the screen 5900 by means of asequential color display method.

That is, the variable light source 5210, comprising a red laser lightsource 5211, a green laser light source 5212 and a blue laser lightsource 5213 (which are not shown in a drawing here) that allowsindependent controls for the light emission states, performs theoperation of dividing one frame of display data into a plurality ofsub-fields (i.e., three sub-fields, that is, red (R), green (G) and blue(B) in the present case) and making each of the red laser light source5211, green laser light source 5212 and blue laser light source 5213emit each respective light in time series at the time band correspondingto the sub-field of each color as described later. Note that the redlaser light source 5211, green laser light source 5212 and blue laserlight source 5213 may alternatively be replaced with light emittingdiodes (LEDs), respectively.

Next is a description of a multi-panel projection apparatus using aplurality of spatial light modulators to continuously modulate theillumination lights with respectively different frequencies using theindividual spatial light modulators and carrying out a color display bysynthesizing the modulated illumination lights, with reference to FIG.31A.

FIG. 31A is a conceptual diagram showing the configuration of amulti-panel projection apparatus according to the embodiment. Theprojection apparatus 5020 is a so-called multiple-plate projectionapparatus comprising a plurality of spatial light modulators 5100, whichis the difference from the above described projection apparatus 5010.Further, the projection apparatus 5020 comprises a control unit 5502 inplace of the control unit 5500.

The projection apparatus 5020 comprises a plurality of spatial lightmodulators 5100, and is equipped with a light separation/synthesisoptical system 5310 between the projection optical system 5400 and eachof the spatial light modulators 5100.

The light separation/synthesis optical system 5310 comprises a TIR prism5311, color separation prism 5312 and color separation prism 5313.

The TIR prism 5311 has the function of leading the illumination light5600 incident from the side of the optical axis of the projectionoptical system 5400 to the spatial light modulator 5100 as incidentlight 5601.

The color separation prism 5312 has the functions of separating red (R)light from an incident light 5601 incident by way of the TIR prism 5311and making the red light incident to the red light-use spatial lightmodulators 5100, and the function of leading the reflection light 5602Rof the red light to the TIR prism 5311.

Likewise, the color separation prism 5313 has the functions ofseparating blue (B) and green (G) lights from the incident light 5601incident by way of the TIR prism 5311 and making them incident to theblue color-use spatial light modulators 5100 and green color-use spatiallight modulators 5100, and the function of leading the reflection light5602 of the green light and blue light to the TIR prism 5311.

Therefore, the spatial light modulations of three colors of R, G and Bare simultaneously performed at three spatial light modulators 5100,respectively, and the reflection lights resulting the respectivemodulations are projected onto the screen 5900 as the projection light5603 by way of the projection optical system 5400, and thus a colordisplay is carried out.

Note that various modifications are conceivable for a lightseparation/synthesis optical system, in lieu of being limited to thelight separation/synthesis optical system 5310.

FIG. 31B is a conceptual diagram showing the configuration of anexemplary modification of a multi-panel projection apparatus accordingto the present embodiment. The projection apparatus 5030 comprises alight separation/synthesis optical system 5320 in place of the abovedescribed light separation/synthesis optical system 5310. The lightseparation/synthesis optical system 5320 comprises a TIR prism 5321 anda cross dichroic mirror 5322.

The TIR prism 5321 has the function of leading an illumination light5600 incident from the lateral direction of the optical axis of theprojection optical system 5400 to the spatial light modulators 5100 asincident light 5601.

The cross dichroic mirror 5322 has the function of separating the lightsof red, blue and green colors from the incident light 5601 incoming fromthe TIR prism 5321, making the incident lights 5601 of the three colorsrespectively enter the red-use, blue-use and green-use spatial lightmodulators 5100, and also converging the reflection lights 5602reflected by the respective color-use spatial light modulators 5100 andleading it to the projection optical system 5400.

FIG. 31C is a conceptual diagram showing the configuration of anotherexemplary modification of a multi-panel projection apparatus accordingto the present embodiment. The projection apparatus 5040 is configured,differently from the above described projection, apparatuses 5020 and5030, to place, so as to be adjacent to one another in the same plane, aplurality of spatial light modulators 5100 corresponding to the threerespective colors R, G and B on one side of a light separation/synthesisoptical system 5330.

This configuration makes it possible to place the plurality of spatiallight modulators 5100, for example, by consolidating them into the samepackaging unit, such as a package, by saving the space.

The light separation/synthesis optical system 5330 comprises a TIR prism5331, a prism 5332 and a prism 5333.

The TIR prism 5331 has the function of leading, to spatial lightmodulators 5100, the illumination light 5600 incident in the lateraldirection of the optical axis of the projection optical system 5400 asincident light 5601.

The prism 5332 has the functions of separating a red color light fromthe incident light 5601 and leading it to the red color-use spatiallight modulator 5100, and also capturing the reflection light 5602 andleading it to the projection optical system 5400.

Likewise, the prism 5333 has the functions of separating the incidentlights of green and blue colors from the incident light 5601, makingthem incident to the individual spatial light modulators 5100 equippedcorrespondently to the respective colors, and capturing the reflectionlights 5602 of the respective colors to lead them to the projectionoptical system 5400.

Note that the multi-panel projection apparatus does not allow anoccurrence of a visual problem such as a color break since theindividual primary colors are constantly projected, unlike the abovedescribed single-panel projection apparatus. Further, a bright image canbe obtained because the light emitted from the light source can beeffectively utilized. On the other hand, there is a problem such as acomplicated adjustment for the positioning of the spatial lightmodulator corresponding to the light of individual color and an increasein the size of the apparatus.

Such is a description of a three-panel projection apparatus using threespatial light modulators as an example of a multi-panel projectionapparatus. The following is a description of a two-panel projectionapparatus using two spatial light modulators (i.e., mirror devices) asanother example of a multi-panel projection apparatus.

FIGS. 29A through 29D show the configuration of a two-panel projectionapparatus 2500 comprising the assembly body 2400, shown in the abovedescribed FIGS. 28A and 28B, which is obtained by one packageaccommodating two mirror devices 2030 and 2040.

The two-panel projection apparatus 2500 does not project only one colorof three colors R, G and B in sequence, nor does it project the R, G andB colors continuously and simultaneously as in the case of a three-panelprojection apparatus. A two-panel projection apparatus projects an imageby means of a projection method for continuously projecting, forexample, a green light source with high visibility and projecting a redlight source and a blue light source in sequence.

The two-panel projection apparatus 2500 is capable of changing overcolors in high speed by means of pulse emission in 180 kHz to 720 kHz bycomprising laser light sources, thereby making it possible to obscureflickers caused by changing over among the light sources of therespective colors.

Further, a projection method for continuously projecting the brightestcolor and changing over the other colors in sequence on the basis of theimage signals can also be adopted. Such projection methods can also beadopted for a configuration making R, G and B lights correspond to therespective mirror devices, as in the three-panel projection method.

FIG. 29A is a front view diagram of a two-panel projection apparatus2500; FIG. 29B is a rear view diagram of the two-panel projectionapparatus 2500; FIG. 29C is a side view diagram of the two-panelprojection apparatus 2500; and FIG. 29D is a plain view diagram of thetwo-panel projection apparatus 2500.

The following is a description of the optical comprisal and principle ofprojection of the two-panel projection apparatus 2500 shown in FIGS. 29Athrough 29D.

The projection apparatus 2500 shown in FIGS. 29A through 29D comprises agreen laser light source 2051, a red laser light source 2052, a bluelaser light source 2053, illumination optical systems 2054 a and 2054 b,two triangular prisms 2056 and 2059, ¼ wavelength plates 2057 a and 2057b, two mirror devices 2030 and 2040 accommodated in a single package, acircuit board 2058, a light guide prism 2064 and a projection lens 2070.

The two triangular prisms 2056 and 2059 are joined together toconstitute one polarization beam splitter prism 2060. Further, thejoined part between the two triangular prisms 2056 and 2059 is providedwith a polarization beam splitter film 2055 or coating. The polarizationbeam splitter prism 2060 primarily fills the role of synthesizing thelight reflected by the two mirror devices 2030 and 2040.

The polarization beam splitter film 2055 is a filter for transmittingonly an S-polarized light and reflecting P-polarized light.

A slope face of the right-angle triangle cone light guide prism 2064 isadhesively attached to the front surface of the polarization beamsplitter prism 2060, with the bottom of the light guide prism 2064facing upward. The green laser light source 2051, the illuminationoptical system 2054 a corresponding to the green laser light source2051, the red laser light source 2052, the blue laser light source 2053,and the illumination optical system 2054 d corresponding to the redlaser light source 2052 and blue laser light source 2053 are equippedbeyond the bottom surface of the light guide prism 2064, with therespective optical axes of the green laser light source 2051, red laserlight source 2052, blue laser light source 2053 being alignedperpendicularly to the bottom surface of the light guide prism 2064.

Here, the light guide prism 2064 is equipped for causing the respectivelights of the green laser light source 2051, red laser light source 2052and blue laser light source 2053 to enter perpendicularly to thepolarization beam splitter prism 2060. Such a light guide prism 2064makes it possible to reduce the amount of the reflection light caused bythe polarization beam splitter prism 2060 when the laser light entersthe polarization beam splitter prism 2060.

Further, ¼ wavelength plates 2057 a and 2057 b are equipped on thebottom surface of the polarization beam splitter prism 2060 on which alight shield layer 2063 is applied in regions other than the areas wherethe light is irradiated on the individual mirror devices 2030 and 2040.Note that the ¼ wavelength plates 2057 a and 2057 b may alternatively beequipped on the cover glass of the package.

Furthermore, a light shield layer 2063 is equipped also on the rearsurface of the polarization beam splitter prism 2060.

Further, the two mirror devices 2030 and 2040, which are accommodated ina single package, are equipped under the ¼ wavelength plates 2057 a and2057 b, and the cover glass of the package is joined to the polarizationbeam splitter prism 2060 by way of a thermal conduction member 2062.This joinder makes it possible to radiate heat from the cover glass ofthe package to the polarization beam splitter prism 2060 by way of thethermal conduction member 2062. Further, the circuit boards 2058comprising a control circuit(s) for controlling the individual mirrordevices 2030 and 2040 equipped respectively on both sides of thepackage.

The mirror devices 2030 and 2040 are respectively placed to form a45-degree angle relative to the four sides of the outer circumference ofthe package. That is, the placement is such that the deflectingdirection of each mirror element of the mirror devices 2030 and 2040 isapproximately orthogonal to the slope face forming the polarization beamsplitter prism 2060 and to the plane on which the reflection lights aresynthesized. In terms of positioning the mirror devices 2030 and 2040 inrelation to the polarization beam splitter prism 2060, a high precisionpositioning of the two mirror devices 2030 and 2040 within the packageby means of the positioning pattern 2016 is very important.

Incidentally, the illumination optical systems 2054 a and 2054 b eachcomprises a convex lens, a concave lens and other components, and theprojection lens 2070 comprises a plurality of lenses and othercomponents.

The following is the principle of projection of the projection apparatus2500 shown in FIGS. 29A through 29D.

In the projection apparatus 2500, the individual laser lights 2065, 2066and 2067 are incident from the front direction and are reflected by thetwo mirror devices 2030 and 2040 toward the rear direction, and then animage is projected by way of the projection lens 2070 located in therear.

Next is a description of the projection principle starting from theincidence of the individual laser lights 2065, 2066 and 2067 to thereflection of the respective laser lights 2065, 2066 and 2067 at the twomirror devices 2030 and 2040 toward the rear direction, with referenceto the front view diagram of the two-panel projection apparatus 2500shown in FIG. 29A.

The respective laser lights 2065, 2066 and 2067 from the S-polarizedgreen laser light source 2051, and the P-polarized red laser lightsource 2052 and blue laser light source 2053 are made to be incident tothe polarization beam splitter prism 2060 by way of the illuminationoptical systems 2054 a and 2054 b respectively corresponding to thelaser lights 2065, and 2066 and 2067, and by way of the light guideprism 2064. Then, having transmitted through the polarization beamsplitter prism 2060, the S-polarized green laser light 2065 and theP-polarized red and blue laser lights 2066 and 2067 are incident to the¼ wavelength plates 2057 a and 2057 b, which are placed on the bottomsurface of the polarization beam splitter prism 2060. Having passingthrough the ¼ wavelength plates 2057 a and 2057 b, the individual laserlights 2065, 2066 and 2067 respectively change the polarization by theamount of ¼ wavelengths to become a circular polarized light state.

Then, having passed through the ¼ wavelength plates 2057 a and 2057 b,the circular polarized green laser light 2065 and the circular polarizedred and blue laser lights 2066 and 2067 respectively incident to the twomirror devices 2030 and 2040 that are accommodated in a single package.The individual laser lights 2065, 2066 and 2067 are modulated andreflected by the correspondingly respective mirror devices so that therotation directions of the circular polarization are reversed.

Next is a description of the projection principle starting from thereflection of individual laser lights 2065, and 2066 and 2067 to theprojection of an image with reference to the rear view diagram of thetwo-panel projection apparatus 2500 shown in FIG. 29B.

The ON light 2068 of the circular polarized green laser and the mixed ONlight 2069 of the circular polarized red and blue lasers, which arereflected by the respective mirror devices 2030 and 2040, passes throughthe ¼ wavelength plates 2057 a and 2057 b again and enter thepolarization beam splitter prism 2060. In this event, the polarizationof the green laser ON light 2068 and that of the mixed red and bluelaser ON light 2069 are respectively changed by the amount of ¼wavelengths to become a linear polarized state with 90-degree differentpolarization axes. That is, the green laser ON light 2068 is changed toa P-polarized light, while the mixed red and blue laser ON light 2069 ischanged to an S-polarized light.

Then, the green laser ON light 2068 and the mixed red and blue laser ONlight 2069 are respectively reflected by the outer side surface of thepolarization beam splitter prism 2060, and the P-polarized green laserON light 2068 is reflected again by the polarization beam splitter film2055. Meanwhile, the S-polarized mixed red and blue laser ON light 2069passes through the polarization beam splitter film 2055. Then, the greenlaser ON light 2068 and red and blue laser mixed ON light 2069 areincident to the projection lens 2070, and thereby a color image isprojected. Note that the optical axes of the respective lights incidentto the projection lens 2070 from the polarization beam splitter prism2060 are desired to be orthogonal to the ejection surface of thepolarization beam splitter prism 2060. Alternatively, there is a viableconfiguration that does not use the ¼ wavelength plates 2057 a and 2057b.

With the configuration and the principle of projection as describedabove, an image can be projected in the two-panel projection apparatus2500 comprising the assembly body 2400 that packages the two mirrordevices 2030 and 2040, which are accommodated in a single package.

FIG. 29C is a side view diagram of the two-panel projection apparatus2500.

The green laser light 2065 emitted from the green laser light source2051 orthogonally enters the light guide prism 2064 via the illuminationoptical system 2054 a. In this event, the reflection of the laser light2065 is minimized by the laser light 2065 orthogonally entering thelight guide prism 2064.

Then, having passed through the light guide prism 2064, the laser light2065 passes through the polarization beam splitter prism 2060 and ¼wavelength plates 2057 a and 2057 b, which are joined to the light guideprism 2064, and then, enters the mirror array 2032 of the mirror device2030.

The mirror array 2032 reflects the laser light 2065 with the deflectionangle of a mirror that puts the reflected light in any of the states,i.e., an ON light state in which the entirety of the reflection light isincident to the projection lens 2070, an intermediate light state inwhich a portion of the reflection light is incident to the projectionlens 2070 and an OFF light state in which no portion of the reflectionlight is incident to the projection lens 2070.

The reflection light of a laser light (i.e., ON light) 2071, from whichthe ON light state is selected, is reflected by the mirror array 2032and will be incident to the projection lens 2070.

A portion of the reflection light of a laser light (i.e., intermediatelight) 2072, from which the intermediate state is selected, is reflectedby the mirror array 2032 and will be incident to the projection lens2070.

Further, the reflection light of a laser light (i.e., OFF light) 2073,from which the OFF light state is selected, is reflected by the mirrorarray 2032 toward the light shield layer 2063, in which the reflectionlight is absorbed.

With this configuration, the laser light enters the projection lens 2070at the maximum light intensity of the ON light, at an intermediateintensity between the ON light and OFF light of the intermediate light,and at the zero intensity of the OFF light. This configuration makes itpossible to project an image in a high level of gradation. Note that theintermediate light state produces a reflection light reflected by amirror of which the deflection angle is regulated between the ON lightstate and OFF light state.

Meanwhile, making the mirror perform a free oscillation causes it tocycle three deflection angles producing the ON light, the intermediatelight and the OFF light, respectively. Here, the controlling of thenumber of free oscillations makes it possible to adjust the lightintensity and obtain an image in higher level of gradation.

FIG. 29D is a plain view diagram of the two-panel projection apparatus2500.

The mirror devices 2030 and 2040 are placed in the package with themrespectively forming an approximately 45-degree angle, on the samehorizontal plane, in relation to the four sides of the outercircumference of the package as shown in FIG. 29D, and thereby the lightin the OFF light state can be absorbed by the light shield layer 2063without allowing the light to be reflected by the slope face of thepolarization beam splitter prism 2060 and the contrast of an image isimproved.

Further, the heat generated inside of the package is conducted to thepolarization beam splitter prism 2060 by way of the thermal conductionmember 2062 and is radiated to the outside therefrom. As such, theconduction of the heat generated in the mirror device to thepolarization beam splitter prism 2060 improves the radiation efficiency.Further, the heat generated by absorbing light is radiated to theoutside instantly because the light shield layer 2063 is exposed to theoutside.

When a mirror element reflects the incident light toward a projectionlens 2070 at an intermediate light intensity (i.e., an intermediatestate) that is the intensity between the ON light and OFF light states,an effective reflection plane needs to be conventionally taken widely inthe longitudinal direction of the slope face of a prism.

In contrast, the projection apparatus 2500 is enabled to provide a wideeffective reflection plane in the thickness direction of thepolarization beam splitter prism 2060 even when the mirror element asdescribed above has the intermediate state. With this configuration, atotal reflection condition with which the reflection light from themirror element is reflected by the slope face of the polarization beamsplitter prism 2060 can be alleviated.

Next is a description of a suitable projection lens when the mirrordevice comprised in the projection apparatus according to the presentembodiment is miniaturized.

If a mirror device of which the diagonal size is 0.95 inches is used fora rear projection system with about 65-inch screen size, a requiredprojection magnification ratio is about 68. If a mirror array of whichthe diagonal size is 0.55 inches is used, a required projectionmagnification ratio is about 118. As such, the projection magnificationincreases in association with the miniaturization of the mirror array.This ushers in the problem of color aberration caused by a projectionlens.

The focal distance of the lens needs to be shortened to increase theprojection magnification. Accordingly, the F number for the projectionlens is set at 5 or higher by comprising a laser light source. Withthis, it is possible to use a projection lens with the F number at 2times, and the focal distance at a half, as compared to the case inwhich a mercury lamp is comprised and a focal distance is 15 mm with theF number at about 2.4 for the projection lens. The usage of a projectionlens with a large F number makes it possible to reduce the outer size ofthe projection lens. This in turn reduces the image size with which alight flux passes through the illumination optical system, therebymaking it possible to suppress a color aberration caused by theprojection lens.

Therefore, in the case of using a laser light source with a mirrordevice miniaturized, to between 0.4 inches and 0.87 inches, thedeflection angle of mirror can be reduced to between ±7 degrees and +5degrees and the F number for a projection lens can be increased.Alternatively, the setting of the numerical aperture NA of anillumination light flux between 0.1 and 0.04 with the deflection angleof mirror maintained at ±13 degrees makes it possible to reflect the OFFlight to a large distance from the projection lens, improving thecontrast of the projection image.

As described above, the projection magnification of a projection lenscan be set at 75× to 120× by reducing the numerical aperture NA of thelight flux emitted from a laser light source, using a mirror device withwhich the deflection angle of mirror is reduced to between ±7 degreesand +5 degrees and in which the mirror array is miniaturized to adiagonal size of 0.4 inches to 0.87 inches, and thereby the F number fora projection lens is increased.

Meanwhile, when a mirror device is moved forward or backward relative tothe optical axis of projection, a distance with which an image blur(i.e., out of focus) of a projected image is permissible is called afocal depth. When an image is projected with a permissible blur in adegree of the mirror size by an optical setup of the same focaldistance, projection magnification and mirror size, a depth of focus isapproximated as follows:

Depth of focus Z=2*(permissible blur)*(F number)

Here, the depth of focus Z is proportional to the F number of aprojection lens. That is, the permissible distance of the shift inpositions of a placed mirror device, relative to the optical axis ofprojection, increases with F number. This factor is represented by therelationship between a permissible circle of confusion and a depth offocus. As an example, where the F number of a projection lens is “8” andthe permissible blur is equivalent to a 10 μm mirror size in the abovedescribed approximation equation, the depth of focus is:

Z=2*10*8=160 [μm]

Further, where a mirror size is 5 μm and an F number is 2.4, the depthof focus is 24 μm. Here, considering the errors of a projection lens andother components of the optical system, the depth of focus is preferredto be no larger than 20 μm or several micrometers or less. With this inmind, when the top or bottom surface of a package substrate is taken asreference, the difference in heights of the reflection on the surface ofmirrors placed respectively on both ends of a mirror array is preferredto be no more than 20 μm.

Further, a blurred image of dust, et cetera, perched on the surface of acover glass can be made invisible by providing a distance between thetop surface of a mirror and the bottom surface of the cover glass with adistance of no less than the value of the depth of focus. It istherefore preferred to provide the distance between the top surface ofthe mirror and the bottom surface of the cover glass with a distance ofat least 20 times, or more, of the mirror size.

Next is a description of the embodiment of a control unit used for aprojection apparatus according to the present embodiment.

FIG. 32 is a block diagram exemplifying a control unit 5500 comprised inthe above described single-panel projection apparatus 5010. Thefollowing is a description of the control unit of the projectionapparatus according to the present embodiment using, as an example, thecontrol unit 5500 comprised in the single-panel projection apparatus5010.

The control unit 5500 comprises a frame memory 5520, an SLM controller5530, a sequencer 5540, a light source control unit 5560 and a lightsource drive circuit 5570.

The sequencer 5540, constituted by a microprocessor and the like,controls the operation timing and the like of the entirety of thecontrol unit 5500 and spatial light modulators 5100.

The frame memory 5520 retains the amount of one frame of input digitalvideo data 5700 incoming from an external device (not shown in a drawingherein), which is connected to a video signal input unit 5510. The inputdigital video data 5700 is updated, moment by moment, every time thedisplay of one frame is completed.

In the case of the single-panel (1××SLM) projection apparatus 5010, oneframe (i.e., a frame 6700-1) of the input digital video data 5700 isconstituted by a plurality of subfields 6701, 6702 and 6703, in a timesequence, corresponding to the respective colors R, G and B asexemplified in FIG. 33A in order to carry out a color display by meansof a color sequence method. The SLM controller 5530 separates the inputdigital video data 5700 read from the frame memory 5520 into a pluralityof subfields 6701, 6702 and 6703, then converts them into mirrorprofiles (i.e., mirror control profiles 6710 and 6720) that are drivessignals for implementing the ON/OFF control and oscillation control forthe mirror of the spatial light modulator 5100 for each sub-field andoutputs the converted mirror profiles to the spatial light modulator5100.

Note that the mirror control profile 6710 is a mirror control profileconsisting of binary data. Here, the binary data means the data in whicheach bit has different weighting and which includes a pulse width inaccordance with the weighting value of each bit. Meanwhile, the mirrorcontrol profile 6720 is a mirror control profile consisting ofnon-binary data. Here, the non-binary data means the data in which eachbit has an equal weighting and which includes a pulse width inaccordance with the number of continuous bits of “1”.

The mirror control profile generated by the SLM controller 5530 is alsoinput to the sequencer 5540, which in turn transmits a light sourceprofile control signal 5800 to the light source control unit 5560 on thebasis of the mirror control profile input from the SLM controller 5530.

The light source control unit 5560 instructs the light source drivecircuit 5570 for the emission timing and light intensity of anillumination light 5600 required of the variable light source 5210corresponding to the driving of the spatial light modulator 5100. Thevariable light source 5210 performs emission so as to emit theillumination light 5600 at the timing and light intensity driven by thelight source drive circuit 5570.

With this control, it is possible to change the brightness of adisplayed pixel through a continuous adjustment of the emission lightintensity of the variable light source 5210 and to control thecharacteristic of the gradations of the display image in the midst ofdriving the spatial light modulator 5100, that is, in the midst ofdisplaying an image onto the screen 5900. The emission light intensityof the variable light source 5210 is adjusted by using a mirror controlprofile used for driving the spatial light modulator 5100, and thereforeno extraneous irradiation occurs, making it possible to suppress theheating from the variable light source 5210 and the power consumptionthereof.

As such, while the description has been provided by exemplifying thecontrol unit 5500 comprised in the single-panel projection apparatus, inthe case of a multi-panel projection apparatus in the meantime, however,a configuration may be such that the SLM controller 5530 and sequencer5540 control a plurality of spatial light modulators 5100. Anotheralternative configuration may be in a manner to equip with a pluralityof SLM controllers, in place of the SLM controller 5530, so as tocontrol the respective spatial light modulators 5100.

Also in the case of a multi-panel projection apparatus, the structure ofthe input digital video data 5700 is also different. In the case of, forexample, the above described multi-panel (3× SLM) projection apparatuses5020, 5030 and 5040, the input digital video data 5700 corresponding toone frame (i.e., the frame 6700-1) display period is constituted by aplurality of fields 6700-2 (i.e., which are equivalent to the subfields6701, 6702 and 6703) corresponding to the respective colors R, G and B,and the fields of the respective colors are output to the plurality ofspatial light modulators 5100, respectively, simultaneously in parallel,as exemplified in FIG. 33B. Also in this case, these are output afterbeing converted into the above described mirror control profile 6710 ormirror control profile 6720 for each of the fields 6700-2 of therespective colors.

Next is a description, in detail, of the embodiment of controlling thevariable light source 5210 with the light source profile control signal5800 corresponding to the mirror control profile.

FIGS. 34A and 34B exemplify an example of the waveform of a mirrorcontrol profile 6720 that is a control signal output from a SLMcontroller 5530 to a spatial light modulator 5100 and an example of thewaveform of a light source pulse pattern 6801 generated by a lightsource control unit 5560 from a light source profile control signal 5800corresponding to the aforementioned mirror control profile 6720.

In this case, one frame of the mirror control profile 6720 isconstituted by the combination of a mirror ON/OFF control 6721 on theframe head side and a mirror oscillation control 6722 on the tail endside and is used for controlling the tilting operation of the mirrorcorresponding to the gray scale of the present frame.

That is, the mirror ON/OFF control 6721 controls the mirror under eitherof the ON state and OFF state, and the mirror oscillation control 6722controls the mirror 5112 under an oscillation state in which itoscillates between the ON state and OFF state.

The present embodiment is configured such that the light source controlunit 5560 performs a control so as to change the frequencies of thepulse emission of the variable light source 5210 in accord with thesignal (i.e., mirror control profile 6720) driving the spatial lightmodulator 5100. The spatial light modulator 5100 is the above describedmirror device 4000 and performs a spatial light modulation of theillumination light 5600 by means of a large number of mirrorscorresponding to pixels to be displayed and of the tilting operation ofthe mirrors.

Note that, for the mirror oscillation control 6722, the pulse emissionfrequency fp of the variable light source 5210 emitting the illuminationlight 5600 is preferably either higher (in the case of the light sourcepulse pattern 6801 shown in FIG. 34A) by ten times, or more, than theoscillation frequency fm of the oscillation control for the mirror, orlower (in the case of the light source pulse pattern 6802 shown in FIG.34B) by one tenth, or less, than the frequency fm. The reason is that,if the oscillation frequency fm of the mirror and the pulse emissionfrequency fp of the variable light source 5210 are close to each other,a humming occurs to possibly hamper a right display of gray scales bymeans of the mirror oscillation control 6722.

FIG. 34C is a chart exemplifying the above described light source pulsepattern 6801, which is shown by enlarging a part corresponding to themirror oscillation control 6722.

The mirror oscillation control 6722 oscillates at an oscillation cycletosc (1/fm), and in contrast the light source pulse pattern 6801 performpulse emission at a pulse emission frequency fp (1/(tp+ti)) with[emission pulse width tp+emission pulse interval ti] as one cycle. Inthis case, the condition is: fp>(fm*10)

That is, in the example of FIG. 34C, about 32 pulses of emission iscarried out during the oscillation cycle tosc of the mirror oscillationcontrol 6722.

As described above, the changing of the frequencies of the pulseemission of the variable light source 5210 makes it possible to adjustthe light intensity of the illumination light 5600 emitted from thevariable light source 5210.

Note that the present invention may be changed in various mannerspossible within the scope of the present invention, in lieu of beinglimited to the configurations exemplified in the above describedembodiments.

1. A mirror device, comprising: a plurality of deflectable mirrors; anelastic member for deflectably supporting the mirror; a drive electrodefor driving the mirror; a control circuit for giving electric charge tothe drive electrode and controlling the deflecting direction of themirror; and a substrate on which the drive electrode and the elasticmember are formed, wherein the drive electrode is placed within an areaon the substrate the mirror is projected on, has an outer formconstituted by sides approximately in parallel to the outer peripherallines of the present mirror and by sides approximately parallel to thedeflection axis of the present mirror, or a form obtained by dividingthe aforementioned outer form into a plurality thereof, and also fillsthe role of a stopper for regulating the deflection angle of the mirror.2. The mirror device according to claim 1, wherein the drive electrodeis equipped with opposite surfaces which are opposite to the mirror andof which the distances from the present mirror are different.
 3. Themirror device according to claim 1, wherein the drive electrode has aplurality of surfaces in parallel to the bottom surface of the mirror.4. The mirror device according to claim 3, wherein the contact part ofthe drive electrode contacting with the mirror or a deflection memberthat deflects with the mirror is any of the border parts of theplurality of surfaces of the drive electrode.
 5. The mirror deviceaccording to claim 1, satisfying the relationship ofd1≧(L1*d2)/L2, where “L1” is the distance between the edge of the driveelectrode on a side close to the deflection axis of the mirror and thepresent deflection axis, “L2” is the distance between the edge of thedrive electrode on a side far from the deflection axis of the mirror andthe present deflection axis, “d1” is the distance between the bottomsurface of the mirror on the edge of the drive electrode on a side closeto the deflection axis of the mirror and the drive electrode, and “d2”is the distance between the bottom surface of the mirror on the edge ofthe drive electrode on a side far from the deflection axis of the mirrorand the drive electrode.
 6. The mirror device according to claim 1,wherein the contact part of the drive electrode contacting with themirror or a deflection member that deflects with the mirror is anywhereother than the edge of the drive electrode on a side far from thedeflection axis of the present mirror.
 7. The mirror device according toclaim 1, wherein the drive electrode has a form so that a contact withthe mirror or a deflection member that deflects with the mirror is apoint contact.
 8. The mirror device according to claim 1, wherein thedrive electrode has a form so that a contact with the mirror or adeflection member that deflects with the mirror is a line contact. 9.The mirror device according to claim 1, wherein the drive electrode hasa form so that a contact with the mirror or a deflection member thatdeflects with the mirror is an area contact.
 10. The mirror deviceaccording to claim 1, wherein the contact part of the drive electrodecontacting with the mirror or a deflection member that deflects with themirror is a slope surface having the same slope angle as the deflectionangle of the mirror.
 11. The mirror device according to claim 1, whereinthere is a plurality of contact parts of the drive electrode contactingwith the mirror or a deflection member that deflects with the mirror.12. The mirror device according to claim 11, wherein a plurality of thecontact parts are individually placed apart from each other by no lessthan 30% of the deflection axis length of the mirror.
 13. The mirrordevice according to claim 1, wherein at least a part of the driveelectrode including the contact part contacting with the mirror or adeflection member that deflects with the mirror is covered with aninsulation member, and the dielectric strength voltage of the insulationmember is no less than 2 times the drive voltage of the mirror.
 14. Themirror device according to claim 13, wherein the dielectric strengthvoltage of the insulation member is no less than 3 volts.
 15. The mirrordevice according to claim 1, wherein the mirror has an approximatesquare form, and the deflection axis of the mirror is on the diagonalline thereof.
 16. The mirror device according to claim 1, wherein thepitch between the adjacent mirrors is between 4 μm and 10 μm.
 17. Themirror device according to claim 1, wherein the deflection angle of themirror is equal to an angle α which is determined by an aperture ratioof a projection optical system satisfying a theoretical resolutiondetermined by the pitch of the adjacent mirrors in a directionprojecting a modulated light to a projection light path, while thedeflection angle is no less than the angle α in a direction other thanthe direction projecting the modulated light to the projection lightpath.
 18. The mirror device according to claim 1, wherein at least apart of the drive electrode including the contact part contacting withthe mirror or a deflection member that deflects with the mirror iscovered with a passivation material.
 19. The mirror device according toclaim 1, wherein the passivation material is a halide.
 20. The mirrordevice according to claim 1, wherein at least a part of the driveelectrode is covered with a low reflection material.
 21. The mirrordevice according to claim 1, wherein at least a part of the driveelectrode is covered with a film having a film thickness of ¼ of thewavelength of the visible light.
 22. A projection apparatus, comprising:a light source; an illumination optical system for condensing theillumination light emitted from the light source and directing thelight; a mirror device array, comprising a plurality of deflectablemirror elements, for modulating the illumination light emitted from thelight source; and a projection optical system for projecting the lightmodulated by the mirror device array, wherein the mirror elementincludes a mirror and a drive electrode for driving the mirror, thedeflection angle of the mirror is determined by the aperture ratio ofthe projection optical system satisfying a theoretical resolution thatis determined on the basis of the pitch of the adjacent mirrors, and thedrive electrode also fills the function of a stopper for regulating thedeflection angle.
 23. The projection apparatus according to claim 22,wherein the deflection angle of the mirror is between 2 degrees and 14degrees relative to the horizontal state of the present mirror.
 24. Aprojection apparatus, comprising: a light source; an illuminationoptical system for condensing the illumination light emitted from thelight source and directing the light; a mirror device array, comprisinga plurality of deflectable mirror elements, for modulating theillumination light emitted from the light source; and a projectionoptical system for projecting the light modulated by the mirror devicearray, wherein the mirror element includes a mirror and a driveelectrode for driving the mirror, the deflection angle of the mirror islarger than an angle that is determined by the aperture ratio of theprojection optical system satisfying a theoretical resolution that isdetermined on the basis of the pitch of the adjacent mirrors, and thedrive electrode also fills the role of a stopper for regulating thedeflection angle.